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 $23.49   4.116%   $24.4568   $24.46   $24.45   $24.50  
  Purchase #2 $43.62   9.443%   $47.739   $47.74   $47.75   $47.70  
  Purchase #3 $34.54   4.288%   $36.0211   $36.02   $36.00   $36.00  
  Purchase #4 $157.27   13.793%   $178.9623   $178.96   $178.95   $179.00  
  Purchase #5 $75.31   10.127%   $82.9366   $82.94   $82.95   $82.90  
  Purchase #6 $246.68   12.617%   $277.8036   $277.80   $277.80   $277.80  
  Purchase #7 $223.85   11.237%   $249.004   $249.00   $249.00   $249.00  
  7 purchase totals = $804.76       $896.9234   $896.92   $896.90   $896.90