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 $149.31   8.320%   $161.7326   $161.73   $161.75   $161.70  
  Purchase #2 $62.98   6.205%   $66.8879   $66.89   $66.90   $66.90  
  Purchase #3 $113.42   5.144%   $119.2543   $119.25   $119.25   $119.30  
  Purchase #4 $187.60   8.641%   $203.8105   $203.81   $203.80   $203.80  
  Purchase #5 $26.47   3.434%   $27.379   $27.38   $27.40   $27.40  
  Purchase #6 $221.80   6.350%   $235.8843   $235.88   $235.90   $235.90  
  Purchase #7 $139.53   6.139%   $148.0957   $148.10   $148.10   $148.10  
  7 purchase totals = $901.11       $963.0443   $963.04   $963.10   $963.10