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 $247.73   10.812%   $274.5146   $274.51   $274.50   $274.50  
  Purchase #2 $118.56   5.578%   $125.1733   $125.17   $125.15   $125.20  
  Purchase #3 $71.25   4.305%   $74.3173   $74.32   $74.30   $74.30  
  Purchase #4 $203.83   3.339%   $210.6359   $210.64   $210.65   $210.60  
  Purchase #5 $58.48   5.236%   $61.542   $61.54   $61.55   $61.50  
  Purchase #6 $124.80   5.670%   $131.8762   $131.88   $131.90   $131.90  
  Purchase #7 $119.80   3.686%   $124.2158   $124.22   $124.20   $124.20  
  7 purchase totals = $944.45       $1,002.2751   $1,002.28   $1,002.25   $1,002.20