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 $31.26   6.292%   $33.2269   $33.23   $33.25   $33.20  
  Purchase #2 $112.86   5.418%   $118.9748   $118.97   $118.95   $119.00  
  Purchase #3 $200.41   6.796%   $214.0299   $214.03   $214.05   $214.00  
  Purchase #4 $229.63   4.423%   $239.7865   $239.79   $239.80   $239.80  
  Purchase #5 $91.32   13.109%   $103.2911   $103.29   $103.30   $103.30  
  Purchase #6 $45.48   5.712%   $48.0778   $48.08   $48.10   $48.10  
  Purchase #7 $216.31   12.825%   $244.0518   $244.05   $244.05   $244.10  
  7 purchase totals = $927.27       $1,001.4388   $1,001.44   $1,001.50   $1,001.50