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 $60.35   11.843%   $67.4973   $67.50   $67.50   $67.50  
  Purchase #2 $110.48   10.199%   $121.7479   $121.75   $121.75   $121.70  
  Purchase #3 $232.78   10.224%   $256.5794   $256.58   $256.60   $256.60  
  Purchase #4 $91.73   11.756%   $102.5138   $102.51   $102.50   $102.50  
  Purchase #5 $174.73   12.502%   $196.5747   $196.57   $196.55   $196.60  
  Purchase #6 $56.84   13.492%   $64.5089   $64.51   $64.50   $64.50  
  Purchase #7 $208.43   5.561%   $220.0208   $220.02   $220.00   $220.00  
  7 purchase totals = $935.34       $1,029.4428   $1,029.44   $1,029.40   $1,029.40