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 $216.81   6.206%   $230.2652   $230.27   $230.25   $230.30  
  Purchase #2 $95.57   10.166%   $105.2856   $105.29   $105.30   $105.30  
  Purchase #3 $179.70   4.439%   $187.6769   $187.68   $187.70   $187.70  
  Purchase #4 $112.53   5.562%   $118.7889   $118.79   $118.80   $118.80  
  Purchase #5 $167.71   3.865%   $174.192   $174.19   $174.20   $174.20  
  Purchase #6 $9.31   6.523%   $9.9173   $9.92   $9.90   $9.90  
  Purchase #7 $71.49   3.585%   $74.0529   $74.05   $74.05   $74.10  
  7 purchase totals = $853.12       $900.1788   $900.19   $900.20   $900.30