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 $160.68   9.871%   $176.5407   $176.54   $176.55   $176.50  
  Purchase #2 $217.49   13.453%   $246.7489   $246.75   $246.75   $246.70  
  Purchase #3 $212.58   10.507%   $234.9158   $234.92   $234.90   $234.90  
  Purchase #4 $120.33   5.344%   $126.7604   $126.76   $126.75   $126.80  
  Purchase #5 $33.85   13.374%   $38.3771   $38.38   $38.40   $38.40  
  Purchase #6 $176.95   11.449%   $197.209   $197.21   $197.20   $197.20  
  Purchase #7 $158.80   10.381%   $175.285   $175.29   $175.30   $175.30  
  7 purchase totals = $1,080.68       $1,195.8369   $1,195.85   $1,195.85   $1,195.80