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 $5.68   6.623%   $6.0562   $6.06   $6.05   $6.10  
  Purchase #2 $24.38   11.291%   $27.1327   $27.13   $27.15   $27.10  
  Purchase #3 $100.81   9.784%   $110.6733   $110.67   $110.65   $110.70  
  Purchase #4 $242.56   9.374%   $265.2976   $265.30   $265.30   $265.30  
  Purchase #5 $215.75   10.531%   $238.4706   $238.47   $238.45   $238.50  
  Purchase #6 $47.50   3.282%   $49.059   $49.06   $49.05   $49.10  
  Purchase #7 $246.55   9.586%   $270.1843   $270.18   $270.20   $270.20  
  7 purchase totals = $883.23       $966.8737   $966.87   $966.85   $967.00