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 $43.97   6.288%   $46.7348   $46.73   $46.75   $46.70  
  Purchase #2 $124.91   10.200%   $137.6508   $137.65   $137.65   $137.70  
  Purchase #3 $75.59   13.288%   $85.6344   $85.63   $85.65   $85.60  
  Purchase #4 $52.82   9.546%   $57.8622   $57.86   $57.85   $57.90  
  Purchase #5 $219.52   6.809%   $234.4671   $234.47   $234.45   $234.50  
  Purchase #6 $13.58   4.681%   $14.2157   $14.22   $14.20   $14.20  
  Purchase #7 $146.51   7.166%   $157.0089   $157.01   $157.00   $157.00  
  7 purchase totals = $676.90       $733.5739   $733.57   $733.55   $733.60