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 $151.92   11.723%   $169.7296   $169.73   $169.75   $169.70  
  Purchase #2 $175.28   8.754%   $190.624   $190.62   $190.60   $190.60  
  Purchase #3 $10.90   13.517%   $12.3734   $12.37   $12.35   $12.40  
  Purchase #4 $74.62   11.598%   $83.2744   $83.27   $83.25   $83.30  
  Purchase #5 $250.86   11.257%   $279.0993   $279.10   $279.10   $279.10  
  Purchase #6 $206.76   8.704%   $224.7564   $224.76   $224.75   $224.80  
  Purchase #7 $59.40   9.662%   $65.1392   $65.14   $65.15   $65.10  
  7 purchase totals = $929.74       $1,024.9963   $1,024.99   $1,024.95   $1,025.00