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 $58.98   11.537%   $65.7845   $65.78   $65.80   $65.80  
  Purchase #2 $90.86   12.307%   $102.0421   $102.04   $102.05   $102.00  
  Purchase #3 $59.60   10.288%   $65.7316   $65.73   $65.75   $65.70  
  Purchase #4 $104.97   12.463%   $118.0524   $118.05   $118.05   $118.10  
  Purchase #5 $108.83   11.801%   $121.673   $121.67   $121.65   $121.70  
  Purchase #6 $46.91   5.823%   $49.6416   $49.64   $49.65   $49.60  
  Purchase #7 $230.33   8.823%   $250.652   $250.65   $250.65   $250.70  
  7 purchase totals = $700.48       $773.5772   $773.56   $773.60   $773.60