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 $124.66   13.770%   $141.8257   $141.83   $141.85   $141.80  
  Purchase #2 $168.48   4.631%   $176.2823   $176.28   $176.30   $176.30  
  Purchase #3 $210.31   12.554%   $236.7123   $236.71   $236.70   $236.70  
  Purchase #4 $125.34   6.105%   $132.992   $132.99   $133.00   $133.00  
  Purchase #5 $159.26   7.591%   $171.3494   $171.35   $171.35   $171.30  
  Purchase #6 $213.95   10.286%   $235.9569   $235.96   $235.95   $236.00  
  Purchase #7 $172.95   4.874%   $181.3796   $181.38   $181.40   $181.40  
  7 purchase totals = $1,174.95       $1,276.4982   $1,276.50   $1,276.55   $1,276.50