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 $71.98   6.378%   $76.5709   $76.57   $76.55   $76.60  
  Purchase #2 $88.42   7.256%   $94.8358   $94.84   $94.85   $94.80  
  Purchase #3 $208.96   8.149%   $225.9882   $225.99   $226.00   $226.00  
  Purchase #4 $229.45   13.690%   $260.8617   $260.86   $260.85   $260.90  
  Purchase #5 $247.78   4.217%   $258.2289   $258.23   $258.25   $258.20  
  Purchase #6 $200.39   9.741%   $219.91   $219.91   $219.90   $219.90  
  Purchase #7 $133.47   11.291%   $148.5401   $148.54   $148.55   $148.50  
  7 purchase totals = $1,180.45       $1,284.9356   $1,284.94   $1,284.95   $1,284.90