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 $176.95   12.639%   $199.3147   $199.31   $199.30   $199.30  
  Purchase #2 $190.42   9.732%   $208.9517   $208.95   $208.95   $209.00  
  Purchase #3 $121.77   7.179%   $130.5119   $130.51   $130.50   $130.50  
  Purchase #4 $188.86   7.290%   $202.6279   $202.63   $202.65   $202.60  
  Purchase #5 $86.77   3.132%   $89.4876   $89.49   $89.50   $89.50  
  Purchase #6 $141.35   7.473%   $151.9131   $151.91   $151.90   $151.90  
  Purchase #7 $207.87   7.685%   $223.8448   $223.84   $223.85   $223.80  
  7 purchase totals = $1,113.99       $1,206.6517   $1,206.64   $1,206.65   $1,206.60