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 $199.25   13.707%   $226.5612   $226.56   $226.55   $226.60  
  Purchase #2 $223.36   9.836%   $245.3297   $245.33   $245.35   $245.30  
  Purchase #3 $43.44   8.198%   $47.0012   $47.00   $47.00   $47.00  
  Purchase #4 $135.49   3.508%   $140.243   $140.24   $140.25   $140.20  
  Purchase #5 $71.79   4.209%   $74.8116   $74.81   $74.80   $74.80  
  Purchase #6 $30.59   12.380%   $34.377   $34.38   $34.40   $34.40  
  Purchase #7 $179.51   11.624%   $200.3762   $200.38   $200.40   $200.40  
  7 purchase totals = $883.43       $968.6999   $968.70   $968.75   $968.70