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 $114.81   10.646%   $127.0327   $127.03   $127.05   $127.00  
  Purchase #2 $220.73   12.260%   $247.7915   $247.79   $247.80   $247.80  
  Purchase #3 $170.46   12.811%   $192.2976   $192.30   $192.30   $192.30  
  Purchase #4 $115.77   4.717%   $121.2309   $121.23   $121.25   $121.20  
  Purchase #5 $140.65   3.353%   $145.366   $145.37   $145.35   $145.40  
  Purchase #6 $48.81   5.764%   $51.6234   $51.62   $51.60   $51.60  
  Purchase #7 $248.88   5.376%   $262.2598   $262.26   $262.25   $262.30  
  7 purchase totals = $1,060.11       $1,147.6019   $1,147.60   $1,147.60   $1,147.60