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 $130.27   3.613%   $134.9767   $134.98   $135.00   $135.00  
  Purchase #2 $159.80   6.538%   $170.2477   $170.25   $170.25   $170.20  
  Purchase #3 $15.30   9.664%   $16.7786   $16.78   $16.80   $16.80  
  Purchase #4 $71.50   6.741%   $76.3198   $76.32   $76.30   $76.30  
  Purchase #5 $50.33   5.775%   $53.2366   $53.24   $53.25   $53.20  
  Purchase #6 $231.26   5.768%   $244.5991   $244.60   $244.60   $244.60  
  Purchase #7 $60.54   7.406%   $65.0236   $65.02   $65.00   $65.00  
  7 purchase totals = $719.00       $761.1821   $761.19   $761.20   $761.10