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 $61.69   4.839%   $64.6752   $64.68   $64.70   $64.70  
  Purchase #2 $174.28   12.445%   $195.9691   $195.97   $195.95   $196.00  
  Purchase #3 $105.49   4.539%   $110.2782   $110.28   $110.30   $110.30  
  Purchase #4 $143.26   6.214%   $152.1622   $152.16   $152.15   $152.20  
  Purchase #5 $217.98   11.119%   $242.2172   $242.22   $242.20   $242.20  
  Purchase #6 $13.68   9.801%   $15.0208   $15.02   $15.00   $15.00  
  Purchase #7 $247.83   3.802%   $257.2525   $257.25   $257.25   $257.30  
  7 purchase totals = $964.21       $1,037.5752   $1,037.58   $1,037.55   $1,037.70