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 $95.56   11.129%   $106.1949   $106.19   $106.20   $106.20  
  Purchase #2 $61.72   8.332%   $66.8625   $66.86   $66.85   $66.90  
  Purchase #3 $237.87   9.237%   $259.8421   $259.84   $259.85   $259.80  
  Purchase #4 $10.75   13.797%   $12.2332   $12.23   $12.25   $12.20  
  Purchase #5 $170.27   9.586%   $186.5921   $186.59   $186.60   $186.60  
  Purchase #6 $96.82   4.687%   $101.358   $101.36   $101.35   $101.40  
  Purchase #7 $35.70   5.781%   $37.7638   $37.76   $37.75   $37.80  
  7 purchase totals = $708.69       $770.8466   $770.83   $770.85   $770.90