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 $65.56   3.774%   $68.0342   $68.03   $68.05   $68.00  
  Purchase #2 $77.25   8.301%   $83.6625   $83.66   $83.65   $83.70  
  Purchase #3 $203.78   6.737%   $217.5087   $217.51   $217.50   $217.50  
  Purchase #4 $24.47   4.551%   $25.5836   $25.58   $25.60   $25.60  
  Purchase #5 $152.63   4.620%   $159.6815   $159.68   $159.70   $159.70  
  Purchase #6 $22.42   8.723%   $24.3757   $24.38   $24.40   $24.40  
  Purchase #7 $17.54   11.137%   $19.4934   $19.49   $19.50   $19.50  
  7 purchase totals = $563.65       $598.3396   $598.33   $598.40   $598.40