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 $192.29   13.197%   $217.6665   $217.67   $217.65   $217.70  
  Purchase #2 $229.42   7.385%   $246.3627   $246.36   $246.35   $246.40  
  Purchase #3 $23.50   7.572%   $25.2794   $25.28   $25.30   $25.30  
  Purchase #4 $130.47   8.799%   $141.9501   $141.95   $141.95   $142.00  
  Purchase #5 $227.31   10.366%   $250.873   $250.87   $250.85   $250.90  
  Purchase #6 $161.78   12.697%   $182.3212   $182.32   $182.30   $182.30  
  Purchase #7 $78.74   5.488%   $83.0613   $83.06   $83.05   $83.10  
  7 purchase totals = $1,043.51       $1,147.5142   $1,147.51   $1,147.45   $1,147.70