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 $62.53   3.869%   $64.9493   $64.95   $64.95   $64.90  
  Purchase #2 $116.68   11.435%   $130.0224   $130.02   $130.00   $130.00  
  Purchase #3 $129.61   4.115%   $134.9435   $134.94   $134.95   $134.90  
  Purchase #4 $236.93   5.732%   $250.5108   $250.51   $250.50   $250.50  
  Purchase #5 $59.60   4.365%   $62.2015   $62.20   $62.20   $62.20  
  Purchase #6 $56.42   8.728%   $61.3443   $61.34   $61.35   $61.30  
  Purchase #7 $101.75   11.168%   $113.1134   $113.11   $113.10   $113.10  
  7 purchase totals = $763.52       $817.0852   $817.07   $817.05   $816.90