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 $35.98   7.321%   $38.6141   $38.61   $38.60   $38.60  
  Purchase #2 $245.84   11.700%   $274.6033   $274.60   $274.60   $274.60  
  Purchase #3 $166.58   9.650%   $182.655   $182.66   $182.65   $182.70  
  Purchase #4 $34.26   8.710%   $37.244   $37.24   $37.25   $37.20  
  Purchase #5 $21.71   4.189%   $22.6194   $22.62   $22.60   $22.60  
  Purchase #6 $113.97   4.192%   $118.7476   $118.75   $118.75   $118.70  
  Purchase #7 $217.51   9.738%   $238.6911   $238.69   $238.70   $238.70  
  7 purchase totals = $835.85       $913.1745   $913.17   $913.15   $913.10