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 $199.69   7.866%   $215.3976   $215.40   $215.40   $215.40  
  Purchase #2 $190.79   4.283%   $198.9615   $198.96   $198.95   $199.00  
  Purchase #3 $53.49   6.149%   $56.7791   $56.78   $56.80   $56.80  
  Purchase #4 $227.87   5.243%   $239.8172   $239.82   $239.80   $239.80  
  Purchase #5 $141.34   11.517%   $157.6181   $157.62   $157.60   $157.60  
  Purchase #6 $239.64   5.409%   $252.6021   $252.60   $252.60   $252.60  
  Purchase #7 $208.58   11.706%   $232.9964   $233.00   $233.00   $233.00  
  7 purchase totals = $1,261.40       $1,354.1720   $1,354.18   $1,354.15   $1,354.20