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 $86.65   13.274%   $98.1519   $98.15   $98.15   $98.20  
  Purchase #2 $77.87   11.254%   $86.6335   $86.63   $86.65   $86.60  
  Purchase #3 $149.73   8.552%   $162.5349   $162.53   $162.55   $162.50  
  Purchase #4 $177.65   4.832%   $186.234   $186.23   $186.25   $186.20  
  Purchase #5 $129.30   3.180%   $133.4117   $133.41   $133.40   $133.40  
  Purchase #6 $157.35   13.826%   $179.1052   $179.11   $179.10   $179.10  
  Purchase #7 $246.93   11.433%   $275.1615   $275.16   $275.15   $275.20  
  7 purchase totals = $1,025.48       $1,121.2327   $1,121.22   $1,121.25   $1,121.20