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 $218.88   10.282%   $241.3852   $241.39   $241.40   $241.40  
  Purchase #2 $40.99   8.196%   $44.3495   $44.35   $44.35   $44.30  
  Purchase #3 $78.71   7.240%   $84.4086   $84.41   $84.40   $84.40  
  Purchase #4 $181.79   6.866%   $194.2717   $194.27   $194.25   $194.30  
  Purchase #5 $197.80   9.851%   $217.2853   $217.29   $217.30   $217.30  
  Purchase #6 $62.35   12.254%   $69.9904   $69.99   $70.00   $70.00  
  Purchase #7 $112.94   5.451%   $119.0964   $119.10   $119.10   $119.10  
  7 purchase totals = $893.46       $970.7871   $970.80   $970.80   $970.80