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 $232.75   9.532%   $254.9357   $254.94   $254.95   $254.90  
  Purchase #2 $175.46   13.268%   $198.74   $198.74   $198.75   $198.70  
  Purchase #3 $41.95   10.623%   $46.4063   $46.41   $46.40   $46.40  
  Purchase #4 $34.43   4.669%   $36.0375   $36.04   $36.05   $36.00  
  Purchase #5 $86.76   9.555%   $95.0499   $95.05   $95.05   $95.00  
  Purchase #6 $96.29   13.336%   $109.1312   $109.13   $109.15   $109.10  
  Purchase #7 $21.96   3.112%   $22.6434   $22.64   $22.65   $22.60  
  7 purchase totals = $689.60       $762.9440   $762.95   $763.00   $762.70