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 $240.26   11.482%   $267.8467   $267.85   $267.85   $267.80  
  Purchase #2 $227.39   3.295%   $234.8825   $234.88   $234.90   $234.90  
  Purchase #3 $62.25   12.110%   $69.7885   $69.79   $69.80   $69.80  
  Purchase #4 $212.30   13.241%   $240.4106   $240.41   $240.40   $240.40  
  Purchase #5 $169.70   7.488%   $182.4071   $182.41   $182.40   $182.40  
  Purchase #6 $62.56   10.584%   $69.1814   $69.18   $69.20   $69.20  
  Purchase #7 $9.38   6.161%   $9.9579   $9.96   $9.95   $10.00  
  7 purchase totals = $983.84       $1,074.4747   $1,074.48   $1,074.50   $1,074.50