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 $49.79   11.820%   $55.6752   $55.68   $55.70   $55.70  
  Purchase #2 $72.48   8.864%   $78.9046   $78.90   $78.90   $78.90  
  Purchase #3 $162.61   4.416%   $169.7909   $169.79   $169.80   $169.80  
  Purchase #4 $88.31   10.485%   $97.5693   $97.57   $97.55   $97.60  
  Purchase #5 $111.92   6.710%   $119.4298   $119.43   $119.45   $119.40  
  Purchase #6 $237.72   10.268%   $262.1291   $262.13   $262.15   $262.10  
  Purchase #7 $250.97   5.674%   $265.21   $265.21   $265.20   $265.20  
  7 purchase totals = $973.80       $1,048.7089   $1,048.71   $1,048.75   $1,048.70