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 $244.86   5.759%   $258.9615   $258.96   $258.95   $259.00  
  Purchase #2 $9.53   8.258%   $10.317   $10.32   $10.30   $10.30  
  Purchase #3 $149.34   13.571%   $169.6069   $169.61   $169.60   $169.60  
  Purchase #4 $61.30   12.853%   $69.1789   $69.18   $69.20   $69.20  
  Purchase #5 $198.27   5.869%   $209.9065   $209.91   $209.90   $209.90  
  Purchase #6 $226.93   12.236%   $254.6972   $254.70   $254.70   $254.70  
  Purchase #7 $123.28   6.726%   $131.5718   $131.57   $131.55   $131.60  
  7 purchase totals = $1,013.51       $1,104.2398   $1,104.25   $1,104.20   $1,104.30