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 $205.29   12.824%   $231.6164   $231.62   $231.60   $231.60  
  Purchase #2 $65.69   12.316%   $73.7804   $73.78   $73.80   $73.80  
  Purchase #3 $82.82   9.204%   $90.4428   $90.44   $90.45   $90.40  
  Purchase #4 $211.72   12.321%   $237.806   $237.81   $237.80   $237.80  
  Purchase #5 $90.42   6.712%   $96.489   $96.49   $96.50   $96.50  
  Purchase #6 $187.62   5.752%   $198.4119   $198.41   $198.40   $198.40  
  Purchase #7 $79.70   7.449%   $85.6369   $85.64   $85.65   $85.60  
  7 purchase totals = $923.26       $1,014.1834   $1,014.19   $1,014.20   $1,014.10