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 $113.97   9.570%   $124.8769   $124.88   $124.90   $124.90  
  Purchase #2 $54.62   7.561%   $58.7498   $58.75   $58.75   $58.70  
  Purchase #3 $163.38   12.872%   $184.4103   $184.41   $184.40   $184.40  
  Purchase #4 $216.96   9.502%   $237.5755   $237.58   $237.60   $237.60  
  Purchase #5 $186.41   3.406%   $192.7591   $192.76   $192.75   $192.80  
  Purchase #6 $128.74   10.649%   $142.4495   $142.45   $142.45   $142.40  
  Purchase #7 $8.83   4.493%   $9.2267   $9.23   $9.25   $9.20  
  7 purchase totals = $872.91       $950.0478   $950.06   $950.10   $950.00