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 $87.66   8.521%   $95.1295   $95.13   $95.15   $95.10  
  Purchase #2 $241.58   12.572%   $271.9514   $271.95   $271.95   $272.00  
  Purchase #3 $22.80   13.150%   $25.7982   $25.80   $25.80   $25.80  
  Purchase #4 $105.61   9.122%   $115.2437   $115.24   $115.25   $115.20  
  Purchase #5 $91.56   6.301%   $97.3292   $97.33   $97.35   $97.30  
  Purchase #6 $239.87   7.797%   $258.5727   $258.57   $258.55   $258.60  
  Purchase #7 $106.32   7.317%   $114.0994   $114.10   $114.10   $114.10  
  7 purchase totals = $895.40       $978.1241   $978.12   $978.15   $978.10