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 $250.26   6.811%   $267.3052   $267.31   $267.30   $267.30  
  Purchase #2 $240.40   12.154%   $269.6182   $269.62   $269.60   $269.60  
  Purchase #3 $185.37   7.164%   $198.6499   $198.65   $198.65   $198.60  
  Purchase #4 $158.66   4.313%   $165.503   $165.50   $165.50   $165.50  
  Purchase #5 $24.29   6.207%   $25.7977   $25.80   $25.80   $25.80  
  Purchase #6 $43.32   9.436%   $47.4077   $47.41   $47.40   $47.40  
  Purchase #7 $91.97   8.196%   $99.5079   $99.51   $99.50   $99.50  
  7 purchase totals = $994.27       $1,073.7896   $1,073.80   $1,073.75   $1,073.70