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 $152.96   10.178%   $168.5283   $168.53   $168.55   $168.50  
  Purchase #2 $249.62   6.402%   $265.6007   $265.60   $265.60   $265.60  
  Purchase #3 $162.79   5.329%   $171.4651   $171.47   $171.45   $171.50  
  Purchase #4 $164.80   6.329%   $175.2302   $175.23   $175.25   $175.20  
  Purchase #5 $29.92   7.177%   $32.0674   $32.07   $32.05   $32.10  
  Purchase #6 $207.46   11.331%   $230.9673   $230.97   $230.95   $231.00  
  Purchase #7 $135.54   11.315%   $150.8764   $150.88   $150.90   $150.90  
  7 purchase totals = $1,103.09       $1,194.7354   $1,194.75   $1,194.75   $1,194.80