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 $87.41   9.434%   $95.6563   $95.66   $95.65   $95.70  
  Purchase #2 $108.56   5.422%   $114.4461   $114.45   $114.45   $114.40  
  Purchase #3 $68.90   12.536%   $77.5373   $77.54   $77.55   $77.50  
  Purchase #4 $160.27   5.784%   $169.54   $169.54   $169.55   $169.50  
  Purchase #5 $103.46   5.379%   $109.0251   $109.03   $109.05   $109.00  
  Purchase #6 $21.87   11.373%   $24.3573   $24.36   $24.35   $24.40  
  Purchase #7 $224.48   7.351%   $240.9815   $240.98   $241.00   $241.00  
  7 purchase totals = $774.95       $831.5436   $831.56   $831.60   $831.50