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 $69.39   5.167%   $72.9754   $72.98   $73.00   $73.00  
  Purchase #2 $49.84   8.199%   $53.9264   $53.93   $53.95   $53.90  
  Purchase #3 $207.80   10.474%   $229.565   $229.57   $229.55   $229.60  
  Purchase #4 $234.54   6.562%   $249.9305   $249.93   $249.95   $249.90  
  Purchase #5 $101.54   12.185%   $113.9126   $113.91   $113.90   $113.90  
  Purchase #6 $122.47   6.180%   $130.0386   $130.04   $130.05   $130.00  
  Purchase #7 $166.76   3.383%   $172.4015   $172.40   $172.40   $172.40  
  7 purchase totals = $952.34       $1,022.7500   $1,022.76   $1,022.80   $1,022.70