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 $146.79   12.431%   $165.0375   $165.04   $165.05   $165.00  
  Purchase #2 $61.73   12.200%   $69.2611   $69.26   $69.25   $69.30  
  Purchase #3 $163.64   11.685%   $182.7613   $182.76   $182.75   $182.80  
  Purchase #4 $98.86   4.316%   $103.1268   $103.13   $103.15   $103.10  
  Purchase #5 $208.85   12.178%   $234.2838   $234.28   $234.30   $234.30  
  Purchase #6 $44.41   9.345%   $48.5601   $48.56   $48.55   $48.60  
  Purchase #7 $221.54   4.674%   $231.8948   $231.89   $231.90   $231.90  
  7 purchase totals = $945.82       $1,034.9254   $1,034.92   $1,034.95   $1,035.00