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 $51.97   9.479%   $56.8962   $56.90   $56.90   $56.90  
  Purchase #2 $226.34   7.784%   $243.9583   $243.96   $243.95   $244.00  
  Purchase #3 $76.77   3.773%   $79.6665   $79.67   $79.65   $79.70  
  Purchase #4 $168.49   3.782%   $174.8623   $174.86   $174.85   $174.90  
  Purchase #5 $83.73   11.545%   $93.3966   $93.40   $93.40   $93.40  
  Purchase #6 $192.51   12.169%   $215.9365   $215.94   $215.95   $215.90  
  Purchase #7 $87.29   7.719%   $94.0279   $94.03   $94.05   $94.00  
  7 purchase totals = $887.10       $958.7443   $958.76   $958.75   $958.80