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 $113.81   7.456%   $122.2957   $122.30   $122.30   $122.30  
  Purchase #2 $197.57   7.743%   $212.8678   $212.87   $212.85   $212.90  
  Purchase #3 $41.76   6.188%   $44.3441   $44.34   $44.35   $44.30  
  Purchase #4 $91.40   6.373%   $97.2249   $97.22   $97.20   $97.20  
  Purchase #5 $230.47   11.243%   $256.3817   $256.38   $256.40   $256.40  
  Purchase #6 $71.90   4.839%   $75.3792   $75.38   $75.40   $75.40  
  Purchase #7 $120.26   4.213%   $125.3266   $125.33   $125.35   $125.30  
  7 purchase totals = $867.17       $933.8200   $933.82   $933.85   $933.80