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 $32.54   8.171%   $35.1988   $35.20   $35.20   $35.20  
  Purchase #2 $220.64   6.490%   $234.9595   $234.96   $234.95   $235.00  
  Purchase #3 $63.73   7.752%   $68.6703   $68.67   $68.65   $68.70  
  Purchase #4 $216.29   7.245%   $231.9602   $231.96   $231.95   $232.00  
  Purchase #5 $74.93   5.186%   $78.8159   $78.82   $78.80   $78.80  
  Purchase #6 $132.63   6.551%   $141.3186   $141.32   $141.30   $141.30  
  Purchase #7 $195.86   10.534%   $216.4919   $216.49   $216.50   $216.50  
  7 purchase totals = $936.62       $1,007.4152   $1,007.42   $1,007.35   $1,007.50