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 $222.54   10.856%   $246.6989   $246.70   $246.70   $246.70  
  Purchase #2 $104.58   13.532%   $118.7318   $118.73   $118.75   $118.70  
  Purchase #3 $174.99   7.581%   $188.256   $188.26   $188.25   $188.30  
  Purchase #4 $236.39   7.168%   $253.3344   $253.33   $253.35   $253.30  
  Purchase #5 $148.71   3.251%   $153.5446   $153.54   $153.55   $153.50  
  Purchase #6 $15.60   5.282%   $16.424   $16.42   $16.40   $16.40  
  Purchase #7 $152.87   10.531%   $168.9687   $168.97   $168.95   $169.00  
  7 purchase totals = $1,055.68       $1,145.9584   $1,145.95   $1,145.95   $1,145.90