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 $75.54   9.465%   $82.6899   $82.69   $82.70   $82.70  
  Purchase #2 $129.44   8.666%   $140.6573   $140.66   $140.65   $140.70  
  Purchase #3 $20.38   10.559%   $22.5319   $22.53   $22.55   $22.50  
  Purchase #4 $245.51   10.753%   $271.9097   $271.91   $271.90   $271.90  
  Purchase #5 $109.95   4.168%   $114.5327   $114.53   $114.55   $114.50  
  Purchase #6 $182.68   5.198%   $192.1757   $192.18   $192.20   $192.20  
  Purchase #7 $194.41   8.579%   $211.0884   $211.09   $211.10   $211.10  
  7 purchase totals = $957.91       $1,035.5856   $1,035.59   $1,035.65   $1,035.60