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 $43.39   8.199%   $46.9475   $46.95   $46.95   $46.90  
  Purchase #2 $217.39   3.449%   $224.8878   $224.89   $224.90   $224.90  
  Purchase #3 $130.56   9.160%   $142.5193   $142.52   $142.50   $142.50  
  Purchase #4 $194.35   8.477%   $210.825   $210.83   $210.85   $210.80  
  Purchase #5 $50.46   13.829%   $57.4381   $57.44   $57.45   $57.40  
  Purchase #6 $119.65   13.531%   $135.8398   $135.84   $135.85   $135.80  
  Purchase #7 $143.78   3.489%   $148.7965   $148.80   $148.80   $148.80  
  7 purchase totals = $899.58       $967.2540   $967.27   $967.30   $967.10