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 $55.84   10.355%   $61.6222   $61.62   $61.60   $61.60  
  Purchase #2 $236.49   4.607%   $247.3851   $247.39   $247.40   $247.40  
  Purchase #3 $64.70   3.203%   $66.7723   $66.77   $66.75   $66.80  
  Purchase #4 $62.39   3.258%   $64.4227   $64.42   $64.40   $64.40  
  Purchase #5 $69.29   11.362%   $77.1627   $77.16   $77.15   $77.20  
  Purchase #6 $121.45   7.535%   $130.6013   $130.60   $130.60   $130.60  
  Purchase #7 $51.50   5.815%   $54.4947   $54.49   $54.50   $54.50  
  7 purchase totals = $661.66       $702.4610   $702.45   $702.40   $702.50