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 $168.64   11.194%   $187.5176   $187.52   $187.50   $187.50  
  Purchase #2 $73.86   3.354%   $76.3373   $76.34   $76.35   $76.30  
  Purchase #3 $44.98   6.317%   $47.8214   $47.82   $47.80   $47.80  
  Purchase #4 $87.83   11.751%   $98.1509   $98.15   $98.15   $98.20  
  Purchase #5 $122.86   7.663%   $132.2748   $132.27   $132.25   $132.30  
  Purchase #6 $182.77   13.622%   $207.6669   $207.67   $207.65   $207.70  
  Purchase #7 $41.34   8.813%   $44.9833   $44.98   $45.00   $45.00  
  7 purchase totals = $722.28       $794.7522   $794.75   $794.70   $794.80