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 $232.77   3.540%   $241.0101   $241.01   $241.00   $241.00  
  Purchase #2 $171.31   9.121%   $186.9352   $186.94   $186.95   $186.90  
  Purchase #3 $76.83   11.107%   $85.3635   $85.36   $85.35   $85.40  
  Purchase #4 $95.33   5.664%   $100.7295   $100.73   $100.75   $100.70  
  Purchase #5 $28.81   5.371%   $30.3574   $30.36   $30.35   $30.40  
  Purchase #6 $142.92   9.485%   $156.476   $156.48   $156.50   $156.50  
  Purchase #7 $223.64   5.112%   $235.0725   $235.07   $235.05   $235.10  
  7 purchase totals = $971.61       $1,035.9442   $1,035.95   $1,035.95   $1,036.00