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 $24.86   7.275%   $26.6686   $26.67   $26.65   $26.70  
  Purchase #2 $122.33   3.624%   $126.7632   $126.76   $126.75   $126.80  
  Purchase #3 $240.84   4.409%   $251.4586   $251.46   $251.45   $251.50  
  Purchase #4 $119.79   10.734%   $132.6483   $132.65   $132.65   $132.60  
  Purchase #5 $249.81   11.205%   $277.8012   $277.80   $277.80   $277.80  
  Purchase #6 $88.87   5.785%   $94.0111   $94.01   $94.00   $94.00  
  Purchase #7 $97.47   10.427%   $107.6332   $107.63   $107.65   $107.60  
  7 purchase totals = $943.97       $1,016.9842   $1,016.98   $1,016.95   $1,017.00