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 $233.46   8.198%   $252.5991   $252.60   $252.60   $252.60  
  Purchase #2 $227.47   6.679%   $242.6627   $242.66   $242.65   $242.70  
  Purchase #3 $120.58   9.553%   $132.099   $132.10   $132.10   $132.10  
  Purchase #4 $232.43   13.285%   $263.3083   $263.31   $263.30   $263.30  
  Purchase #5 $134.94   9.608%   $147.905   $147.91   $147.90   $147.90  
  Purchase #6 $222.63   11.653%   $248.5731   $248.57   $248.55   $248.60  
  Purchase #7 $197.25   3.174%   $203.5107   $203.51   $203.50   $203.50  
  7 purchase totals = $1,368.76       $1,490.6579   $1,490.66   $1,490.60   $1,490.70