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 $240.50   11.283%   $267.6356   $267.64   $267.65   $267.60  
  Purchase #2 $100.49   9.315%   $109.8506   $109.85   $109.85   $109.90  
  Purchase #3 $233.82   13.444%   $265.2548   $265.25   $265.25   $265.30  
  Purchase #4 $199.64   5.752%   $211.1233   $211.12   $211.10   $211.10  
  Purchase #5 $160.40   5.374%   $169.0199   $169.02   $169.00   $169.00  
  Purchase #6 $174.33   6.150%   $185.0513   $185.05   $185.05   $185.10  
  Purchase #7 $79.46   11.482%   $88.5836   $88.58   $88.60   $88.60  
  7 purchase totals = $1,188.64       $1,296.5191   $1,296.51   $1,296.50   $1,296.60