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 $239.85   11.207%   $266.73   $266.73   $266.75   $266.70  
  Purchase #2 $238.88   6.756%   $255.0187   $255.02   $255.00   $255.00  
  Purchase #3 $27.75   10.659%   $30.7079   $30.71   $30.70   $30.70  
  Purchase #4 $86.89   9.317%   $94.9855   $94.99   $95.00   $95.00  
  Purchase #5 $223.46   3.266%   $230.7582   $230.76   $230.75   $230.80  
  Purchase #6 $114.79   9.736%   $125.966   $125.97   $125.95   $126.00  
  Purchase #7 $220.73   12.454%   $248.2197   $248.22   $248.20   $248.20  
  7 purchase totals = $1,152.35       $1,252.3860   $1,252.40   $1,252.35   $1,252.40