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 $101.89   5.202%   $107.1903   $107.19   $107.20   $107.20  
  Purchase #2 $200.58   6.467%   $213.5515   $213.55   $213.55   $213.60  
  Purchase #3 $52.68   5.333%   $55.4894   $55.49   $55.50   $55.50  
  Purchase #4 $101.85   12.231%   $114.3073   $114.31   $114.30   $114.30  
  Purchase #5 $177.67   8.607%   $192.9621   $192.96   $192.95   $193.00  
  Purchase #6 $10.70   12.437%   $12.0308   $12.03   $12.05   $12.00  
  Purchase #7 $195.27   10.389%   $215.5566   $215.56   $215.55   $215.60  
  7 purchase totals = $840.64       $911.0880   $911.09   $911.10   $911.20