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 $154.50   6.491%   $164.5286   $164.53   $164.55   $164.50  
  Purchase #2 $187.88   6.733%   $200.53   $200.53   $200.55   $200.50  
  Purchase #3 $238.26   13.269%   $269.8747   $269.87   $269.85   $269.90  
  Purchase #4 $231.90   9.545%   $254.0349   $254.03   $254.05   $254.00  
  Purchase #5 $18.90   3.801%   $19.6184   $19.62   $19.60   $19.60  
  Purchase #6 $176.74   5.276%   $186.0648   $186.06   $186.05   $186.10  
  Purchase #7 $218.44   6.654%   $232.975   $232.98   $233.00   $233.00  
  7 purchase totals = $1,226.62       $1,327.6264   $1,327.62   $1,327.65   $1,327.60