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 $77.30   11.657%   $86.3109   $86.31   $86.30   $86.30  
  Purchase #2 $92.95   12.598%   $104.6598   $104.66   $104.65   $104.70  
  Purchase #3 $245.94   10.610%   $272.0342   $272.03   $272.05   $272.00  
  Purchase #4 $221.88   10.718%   $245.6611   $245.66   $245.65   $245.70  
  Purchase #5 $195.97   9.695%   $214.9693   $214.97   $214.95   $215.00  
  Purchase #6 $22.76   3.617%   $23.5832   $23.58   $23.60   $23.60  
  Purchase #7 $197.26   3.621%   $204.4028   $204.40   $204.40   $204.40  
  7 purchase totals = $1,054.06       $1,151.6213   $1,151.61   $1,151.60   $1,151.70