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 $68.51   8.334%   $74.2196   $74.22   $74.20   $74.20  
  Purchase #2 $162.50   7.174%   $174.1578   $174.16   $174.15   $174.20  
  Purchase #3 $91.73   4.255%   $95.6331   $95.63   $95.65   $95.60  
  Purchase #4 $154.35   13.345%   $174.948   $174.95   $174.95   $174.90  
  Purchase #5 $171.36   12.406%   $192.6189   $192.62   $192.60   $192.60  
  Purchase #6 $117.51   7.659%   $126.5101   $126.51   $126.50   $126.50  
  Purchase #7 $200.82   13.262%   $227.4527   $227.45   $227.45   $227.50  
  7 purchase totals = $966.78       $1,065.5402   $1,065.54   $1,065.50   $1,065.50