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 $83.56   3.151%   $86.193   $86.19   $86.20   $86.20  
  Purchase #2 $65.47   11.165%   $72.7797   $72.78   $72.80   $72.80  
  Purchase #3 $161.57   9.443%   $176.8271   $176.83   $176.85   $176.80  
  Purchase #4 $214.47   8.769%   $233.2769   $233.28   $233.30   $233.30  
  Purchase #5 $203.54   11.703%   $227.3603   $227.36   $227.35   $227.40  
  Purchase #6 $206.93   9.664%   $226.9277   $226.93   $226.95   $226.90  
  Purchase #7 $136.76   12.864%   $154.3528   $154.35   $154.35   $154.40  
  7 purchase totals = $1,072.30       $1,177.7175   $1,177.72   $1,177.80   $1,177.80