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 $92.82   3.330%   $95.9109   $95.91   $95.90   $95.90  
  Purchase #2 $151.93   8.675%   $165.1099   $165.11   $165.10   $165.10  
  Purchase #3 $238.38   8.110%   $257.7126   $257.71   $257.70   $257.70  
  Purchase #4 $203.27   9.541%   $222.664   $222.66   $222.65   $222.70  
  Purchase #5 $27.89   6.191%   $29.6167   $29.62   $29.60   $29.60  
  Purchase #6 $250.50   11.508%   $279.3275   $279.33   $279.35   $279.30  
  Purchase #7 $69.44   7.340%   $74.5369   $74.54   $74.55   $74.50  
  7 purchase totals = $1,034.23       $1,124.8785   $1,124.88   $1,124.85   $1,124.80