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 $121.57   10.663%   $134.533   $134.53   $134.55   $134.50  
  Purchase #2 $237.48   11.705%   $265.277   $265.28   $265.30   $265.30  
  Purchase #3 $229.53   3.129%   $236.712   $236.71   $236.70   $236.70  
  Purchase #4 $23.93   7.711%   $25.7752   $25.78   $25.80   $25.80  
  Purchase #5 $80.98   6.354%   $86.1255   $86.13   $86.15   $86.10  
  Purchase #6 $124.91   8.767%   $135.8609   $135.86   $135.85   $135.90  
  Purchase #7 $68.72   10.491%   $75.9294   $75.93   $75.95   $75.90  
  7 purchase totals = $887.12       $960.2130   $960.22   $960.30   $960.20