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 $202.71   11.131%   $225.2737   $225.27   $225.25   $225.30  
  Purchase #2 $153.63   7.560%   $165.2444   $165.24   $165.25   $165.20  
  Purchase #3 $184.90   8.668%   $200.9271   $200.93   $200.95   $200.90  
  Purchase #4 $177.49   11.818%   $198.4658   $198.47   $198.45   $198.50  
  Purchase #5 $117.43   5.854%   $124.3044   $124.30   $124.30   $124.30  
  Purchase #6 $194.63   11.266%   $216.557   $216.56   $216.55   $216.60  
  Purchase #7 $119.30   5.624%   $126.0094   $126.01   $126.00   $126.00  
  7 purchase totals = $1,150.09       $1,256.7818   $1,256.78   $1,256.75   $1,256.80