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 $160.64   13.391%   $182.1513   $182.15   $182.15   $182.20  
  Purchase #2 $56.94   4.678%   $59.6037   $59.60   $59.60   $59.60  
  Purchase #3 $124.66   5.494%   $131.5088   $131.51   $131.50   $131.50  
  Purchase #4 $24.45   6.204%   $25.9669   $25.97   $25.95   $26.00  
  Purchase #5 $123.31   13.634%   $140.1221   $140.12   $140.10   $140.10  
  Purchase #6 $210.31   6.545%   $224.0748   $224.07   $224.05   $224.10  
  Purchase #7 $217.42   9.559%   $238.2032   $238.20   $238.20   $238.20  
  7 purchase totals = $917.73       $1,001.6308   $1,001.62   $1,001.55   $1,001.70