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 $222.98   5.471%   $235.1792   $235.18   $235.20   $235.20  
  Purchase #2 $239.76   6.187%   $254.594   $254.59   $254.60   $254.60  
  Purchase #3 $58.50   6.205%   $62.1299   $62.13   $62.15   $62.10  
  Purchase #4 $87.44   12.792%   $98.6253   $98.63   $98.65   $98.60  
  Purchase #5 $218.63   10.639%   $241.89   $241.89   $241.90   $241.90  
  Purchase #6 $7.31   8.269%   $7.9145   $7.91   $7.90   $7.90  
  Purchase #7 $31.48   10.624%   $34.8244   $34.82   $34.80   $34.80  
  7 purchase totals = $866.10       $935.1573   $935.15   $935.20   $935.10