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 $50.66   3.862%   $52.6165   $52.62   $52.60   $52.60  
  Purchase #2 $44.36   6.732%   $47.3463   $47.35   $47.35   $47.30  
  Purchase #3 $239.96   9.290%   $262.2523   $262.25   $262.25   $262.30  
  Purchase #4 $14.32   4.821%   $15.0104   $15.01   $15.00   $15.00  
  Purchase #5 $62.55   5.229%   $65.8207   $65.82   $65.80   $65.80  
  Purchase #6 $218.94   12.148%   $245.5368   $245.54   $245.55   $245.50  
  Purchase #7 $234.37   9.199%   $255.9297   $255.93   $255.95   $255.90  
  7 purchase totals = $865.16       $944.5127   $944.52   $944.50   $944.40