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 $64.55   10.822%   $71.5356   $71.54   $71.55   $71.50  
  Purchase #2 $223.49   5.587%   $235.9764   $235.98   $236.00   $236.00  
  Purchase #3 $239.64   12.861%   $270.4601   $270.46   $270.45   $270.50  
  Purchase #4 $235.33   9.292%   $257.1969   $257.20   $257.20   $257.20  
  Purchase #5 $55.56   4.796%   $58.2247   $58.22   $58.20   $58.20  
  Purchase #6 $195.37   10.478%   $215.8409   $215.84   $215.85   $215.80  
  Purchase #7 $155.63   12.389%   $174.911   $174.91   $174.90   $174.90  
  7 purchase totals = $1,169.57       $1,284.1456   $1,284.15   $1,284.15   $1,284.10