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 $75.76   13.658%   $86.1073   $86.11   $86.10   $86.10  
  Purchase #2 $164.97   10.649%   $182.5377   $182.54   $182.55   $182.50  
  Purchase #3 $217.70   7.801%   $234.6828   $234.68   $234.70   $234.70  
  Purchase #4 $85.80   6.203%   $91.1222   $91.12   $91.10   $91.10  
  Purchase #5 $104.80   11.708%   $117.07   $117.07   $117.05   $117.10  
  Purchase #6 $205.26   5.853%   $217.2739   $217.27   $217.25   $217.30  
  Purchase #7 $116.66   5.541%   $123.1241   $123.12   $123.10   $123.10  
  7 purchase totals = $970.95       $1,051.9180   $1,051.91   $1,051.85   $1,051.90