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 $116.67   13.170%   $132.0354   $132.04   $132.05   $132.00  
  Purchase #2 $57.71   10.433%   $63.7309   $63.73   $63.75   $63.70  
  Purchase #3 $32.76   9.205%   $35.7756   $35.78   $35.80   $35.80  
  Purchase #4 $247.60   12.792%   $279.273   $279.27   $279.25   $279.30  
  Purchase #5 $165.40   6.293%   $175.8086   $175.81   $175.80   $175.80  
  Purchase #6 $175.35   9.596%   $192.1766   $192.18   $192.20   $192.20  
  Purchase #7 $59.49   5.803%   $62.9422   $62.94   $62.95   $62.90  
  7 purchase totals = $854.98       $941.7423   $941.75   $941.80   $941.70