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 $119.79   4.534%   $125.2213   $125.22   $125.20   $125.20  
  Purchase #2 $227.49   10.297%   $250.9146   $250.91   $250.90   $250.90  
  Purchase #3 $51.26   10.492%   $56.6382   $56.64   $56.65   $56.60  
  Purchase #4 $241.88   10.422%   $267.0887   $267.09   $267.10   $267.10  
  Purchase #5 $237.47   13.358%   $269.1912   $269.19   $269.20   $269.20  
  Purchase #6 $19.86   8.451%   $21.5384   $21.54   $21.55   $21.50  
  Purchase #7 $241.42   9.800%   $265.0792   $265.08   $265.10   $265.10  
  7 purchase totals = $1,139.17       $1,255.6716   $1,255.67   $1,255.70   $1,255.60