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 $239.36   3.464%   $247.6514   $247.65   $247.65   $247.70  
  Purchase #2 $231.75   4.476%   $242.1231   $242.12   $242.10   $242.10  
  Purchase #3 $95.64   5.619%   $101.014   $101.01   $101.00   $101.00  
  Purchase #4 $232.79   8.836%   $253.3593   $253.36   $253.35   $253.40  
  Purchase #5 $233.64   11.805%   $261.2212   $261.22   $261.20   $261.20  
  Purchase #6 $66.73   6.858%   $71.3063   $71.31   $71.30   $71.30  
  Purchase #7 $56.94   13.819%   $64.8085   $64.81   $64.80   $64.80  
  7 purchase totals = $1,156.85       $1,241.4838   $1,241.48   $1,241.40   $1,241.50