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 $46.94   12.790%   $52.9436   $52.94   $52.95   $52.90  
  Purchase #2 $248.64   3.406%   $257.1087   $257.11   $257.10   $257.10  
  Purchase #3 $127.81   3.354%   $132.0967   $132.10   $132.10   $132.10  
  Purchase #4 $171.38   6.788%   $183.0133   $183.01   $183.00   $183.00  
  Purchase #5 $60.80   13.834%   $69.2111   $69.21   $69.20   $69.20  
  Purchase #6 $81.31   4.512%   $84.9787   $84.98   $85.00   $85.00  
  Purchase #7 $155.49   9.666%   $170.5197   $170.52   $170.50   $170.50  
  7 purchase totals = $892.37       $949.8718   $949.87   $949.85   $949.80