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 $86.99   8.345%   $94.2493   $94.25   $94.25   $94.20  
  Purchase #2 $107.58   7.218%   $115.3451   $115.35   $115.35   $115.30  
  Purchase #3 $119.86   7.446%   $128.7848   $128.78   $128.80   $128.80  
  Purchase #4 $188.81   3.670%   $195.7393   $195.74   $195.75   $195.70  
  Purchase #5 $157.44   6.541%   $167.7382   $167.74   $167.75   $167.70  
  Purchase #6 $68.80   6.575%   $73.3236   $73.32   $73.30   $73.30  
  Purchase #7 $248.70   13.864%   $283.1798   $283.18   $283.20   $283.20  
  7 purchase totals = $978.18       $1,058.3601   $1,058.36   $1,058.40   $1,058.20