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 $49.30   11.662%   $55.0494   $55.05   $55.05   $55.00  
  Purchase #2 $69.26   8.526%   $75.1651   $75.17   $75.15   $75.20  
  Purchase #3 $114.36   4.645%   $119.672   $119.67   $119.65   $119.70  
  Purchase #4 $215.26   12.243%   $241.6143   $241.61   $241.60   $241.60  
  Purchase #5 $235.70   11.189%   $262.0725   $262.07   $262.05   $262.10  
  Purchase #6 $175.58   9.746%   $192.692   $192.69   $192.70   $192.70  
  Purchase #7 $66.39   7.725%   $71.5186   $71.52   $71.50   $71.50  
  7 purchase totals = $925.85       $1,017.7839   $1,017.78   $1,017.70   $1,017.80