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 $67.68   13.110%   $76.5528   $76.55   $76.55   $76.60  
  Purchase #2 $246.57   3.610%   $255.4712   $255.47   $255.45   $255.50  
  Purchase #3 $249.89   9.158%   $272.7749   $272.77   $272.75   $272.80  
  Purchase #4 $187.32   9.842%   $205.756   $205.76   $205.75   $205.80  
  Purchase #5 $242.51   4.237%   $252.7851   $252.79   $252.80   $252.80  
  Purchase #6 $58.89   5.219%   $61.9635   $61.96   $61.95   $62.00  
  Purchase #7 $156.46   13.677%   $177.859   $177.86   $177.85   $177.90  
  7 purchase totals = $1,209.32       $1,303.1625   $1,303.16   $1,303.10   $1,303.40