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 $34.84   6.207%   $37.0025   $37.00   $37.00   $37.00  
  Purchase #2 $62.63   10.118%   $68.9669   $68.97   $68.95   $69.00  
  Purchase #3 $63.69   13.117%   $72.0442   $72.04   $72.05   $72.00  
  Purchase #4 $166.40   10.414%   $183.7289   $183.73   $183.75   $183.70  
  Purchase #5 $106.99   10.512%   $118.2368   $118.24   $118.25   $118.20  
  Purchase #6 $117.28   11.761%   $131.0733   $131.07   $131.05   $131.10  
  Purchase #7 $76.54   9.313%   $83.6682   $83.67   $83.65   $83.70  
  7 purchase totals = $628.37       $694.7208   $694.72   $694.70   $694.70