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 $36.98   11.269%   $41.1473   $41.15   $41.15   $41.10  
  Purchase #2 $127.97   10.627%   $141.5694   $141.57   $141.55   $141.60  
  Purchase #3 $137.45   11.428%   $153.1578   $153.16   $153.15   $153.20  
  Purchase #4 $210.70   9.163%   $230.0064   $230.01   $230.00   $230.00  
  Purchase #5 $231.98   10.780%   $256.9874   $256.99   $257.00   $257.00  
  Purchase #6 $8.42   11.858%   $9.4184   $9.42   $9.40   $9.40  
  Purchase #7 $76.46   7.482%   $82.1807   $82.18   $82.20   $82.20  
  7 purchase totals = $829.96       $914.4674   $914.48   $914.45   $914.50