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 $69.60   6.578%   $74.1783   $74.18   $74.20   $74.20  
  Purchase #2 $84.92   13.274%   $96.1923   $96.19   $96.20   $96.20  
  Purchase #3 $246.96   13.283%   $279.7637   $279.76   $279.75   $279.80  
  Purchase #4 $24.68   8.327%   $26.7351   $26.74   $26.75   $26.70  
  Purchase #5 $163.42   11.756%   $182.6317   $182.63   $182.65   $182.60  
  Purchase #6 $139.66   9.494%   $152.9193   $152.92   $152.90   $152.90  
  Purchase #7 $130.82   6.743%   $139.6412   $139.64   $139.65   $139.60  
  7 purchase totals = $860.06       $952.0616   $952.06   $952.10   $952.00