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 $60.83   11.402%   $67.7658   $67.77   $67.75   $67.80  
  Purchase #2 $193.59   11.545%   $215.94   $215.94   $215.95   $215.90  
  Purchase #3 $35.44   7.770%   $38.1937   $38.19   $38.20   $38.20  
  Purchase #4 $209.84   8.874%   $228.4612   $228.46   $228.45   $228.50  
  Purchase #5 $151.94   10.772%   $168.307   $168.31   $168.30   $168.30  
  Purchase #6 $85.94   11.758%   $96.0448   $96.04   $96.05   $96.00  
  Purchase #7 $116.36   8.194%   $125.8945   $125.89   $125.90   $125.90  
  7 purchase totals = $853.94       $940.6070   $940.60   $940.60   $940.60