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 $225.68   6.811%   $241.0511   $241.05   $241.05   $241.10  
  Purchase #2 $119.79   5.745%   $126.6719   $126.67   $126.65   $126.70  
  Purchase #3 $61.77   8.240%   $66.8598   $66.86   $66.85   $66.90  
  Purchase #4 $135.46   4.809%   $141.9743   $141.97   $141.95   $142.00  
  Purchase #5 $145.49   9.379%   $159.1355   $159.14   $159.15   $159.10  
  Purchase #6 $245.77   9.553%   $269.2484   $269.25   $269.25   $269.20  
  Purchase #7 $209.27   12.851%   $236.1633   $236.16   $236.15   $236.20  
  7 purchase totals = $1,143.23       $1,241.1043   $1,241.10   $1,241.05   $1,241.20