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 $188.49   7.566%   $202.7512   $202.75   $202.75   $202.80  
  Purchase #2 $166.65   10.805%   $184.6565   $184.66   $184.65   $184.70  
  Purchase #3 $31.45   5.645%   $33.2254   $33.23   $33.25   $33.20  
  Purchase #4 $24.94   13.407%   $28.2837   $28.28   $28.30   $28.30  
  Purchase #5 $169.59   8.620%   $184.2087   $184.21   $184.20   $184.20  
  Purchase #6 $115.90   12.830%   $130.77   $130.77   $130.75   $130.80  
  Purchase #7 $97.92   13.406%   $111.0472   $111.05   $111.05   $111.00  
  7 purchase totals = $794.94       $874.9427   $874.95   $874.95   $875.00