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 $247.95   9.643%   $271.8598   $271.86   $271.85   $271.90  
  Purchase #2 $236.77   11.606%   $264.2495   $264.25   $264.25   $264.20  
  Purchase #3 $49.54   9.572%   $54.282   $54.28   $54.30   $54.30  
  Purchase #4 $58.47   5.179%   $61.4982   $61.50   $61.50   $61.50  
  Purchase #5 $204.46   8.348%   $221.5283   $221.53   $221.55   $221.50  
  Purchase #6 $149.29   8.138%   $161.4392   $161.44   $161.45   $161.40  
  Purchase #7 $185.64   4.481%   $193.9585   $193.96   $193.95   $194.00  
  7 purchase totals = $1,132.12       $1,228.8155   $1,228.82   $1,228.85   $1,228.80