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 $65.76   11.807%   $73.5243   $73.52   $73.50   $73.50  
  Purchase #2 $233.53   6.729%   $249.2442   $249.24   $249.25   $249.20  
  Purchase #3 $243.43   5.564%   $256.9744   $256.97   $256.95   $257.00  
  Purchase #4 $228.30   13.130%   $258.2758   $258.28   $258.30   $258.30  
  Purchase #5 $169.95   5.260%   $178.8894   $178.89   $178.90   $178.90  
  Purchase #6 $179.76   6.456%   $191.3653   $191.37   $191.35   $191.40  
  Purchase #7 $93.82   3.121%   $96.7481   $96.75   $96.75   $96.70  
  7 purchase totals = $1,214.55       $1,305.0215   $1,305.02   $1,305.00   $1,305.00