Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $106.89   12.244%   $119.9776   $119.98   $120.00   $120.00  
  Purchase #2 $159.74   7.396%   $171.5544   $171.55   $171.55   $171.60  
  Purchase #3 $211.73   3.106%   $218.3063   $218.31   $218.30   $218.30  
  Purchase #4 $244.69   12.137%   $274.388   $274.39   $274.40   $274.40  
  Purchase #5 $184.63   11.366%   $205.615   $205.62   $205.60   $205.60  
  Purchase #6 $231.98   13.264%   $262.7498   $262.75   $262.75   $262.70  
  Purchase #7 $223.64   8.175%   $241.9226   $241.92   $241.90   $241.90  
  7 purchase totals = $1,363.30       $1,494.5137   $1,494.52   $1,494.50   $1,494.50