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 $172.40   9.125%   $188.1315   $188.13   $188.15   $188.10  
  Purchase #2 $226.49   3.317%   $234.0027   $234.00   $234.00   $234.00  
  Purchase #3 $36.41   9.356%   $39.8165   $39.82   $39.80   $39.80  
  Purchase #4 $168.63   3.767%   $174.9823   $174.98   $175.00   $175.00  
  Purchase #5 $5.35   8.316%   $5.7949   $5.79   $5.80   $5.80  
  Purchase #6 $42.34   11.606%   $47.254   $47.25   $47.25   $47.30  
  Purchase #7 $66.58   5.214%   $70.0515   $70.05   $70.05   $70.10  
  7 purchase totals = $718.20       $760.0334   $760.02   $760.05   $760.10