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 $21.26   7.638%   $22.8838   $22.88   $22.90   $22.90  
  Purchase #2 $174.76   10.324%   $192.8022   $192.80   $192.80   $192.80  
  Purchase #3 $13.53   10.532%   $14.955   $14.96   $14.95   $15.00  
  Purchase #4 $134.92   5.363%   $142.1558   $142.16   $142.15   $142.20  
  Purchase #5 $70.87   4.586%   $74.1201   $74.12   $74.10   $74.10  
  Purchase #6 $105.59   12.686%   $118.9851   $118.99   $119.00   $119.00  
  Purchase #7 $223.93   9.238%   $244.6167   $244.62   $244.60   $244.60  
  7 purchase totals = $744.86       $810.5187   $810.53   $810.50   $810.60