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 $115.67   6.826%   $123.5656   $123.57   $123.55   $123.60  
  Purchase #2 $219.26   11.130%   $243.6636   $243.66   $243.65   $243.70  
  Purchase #3 $163.83   10.848%   $181.6023   $181.60   $181.60   $181.60  
  Purchase #4 $107.78   7.241%   $115.5843   $115.58   $115.60   $115.60  
  Purchase #5 $161.68   8.467%   $175.3694   $175.37   $175.35   $175.40  
  Purchase #6 $246.44   6.622%   $262.7593   $262.76   $262.75   $262.80  
  Purchase #7 $188.37   5.331%   $198.412   $198.41   $198.40   $198.40  
  7 purchase totals = $1,203.03       $1,300.9565   $1,300.95   $1,300.90   $1,301.10