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 $47.61   12.618%   $53.6174   $53.62   $53.60   $53.60  
  Purchase #2 $150.73   5.310%   $158.7338   $158.73   $158.75   $158.70  
  Purchase #3 $65.55   4.796%   $68.6938   $68.69   $68.70   $68.70  
  Purchase #4 $31.73   13.715%   $36.0818   $36.08   $36.10   $36.10  
  Purchase #5 $95.28   4.677%   $99.7362   $99.74   $99.75   $99.70  
  Purchase #6 $141.84   7.334%   $152.2425   $152.24   $152.25   $152.20  
  Purchase #7 $146.42   11.852%   $163.7737   $163.77   $163.75   $163.80  
  7 purchase totals = $679.16       $732.8792   $732.87   $732.90   $732.80