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 $93.61   8.456%   $101.5257   $101.53   $101.55   $101.50  
  Purchase #2 $237.27   12.741%   $267.5006   $267.50   $267.50   $267.50  
  Purchase #3 $233.31   8.276%   $252.6187   $252.62   $252.60   $252.60  
  Purchase #4 $64.75   6.364%   $68.8707   $68.87   $68.85   $68.90  
  Purchase #5 $25.51   5.604%   $26.9396   $26.94   $26.95   $26.90  
  Purchase #6 $93.65   7.245%   $100.4349   $100.43   $100.45   $100.40  
  Purchase #7 $41.31   11.790%   $46.1804   $46.18   $46.20   $46.20  
  7 purchase totals = $789.41       $864.0706   $864.07   $864.10   $864.00