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 $85.34   11.755%   $95.3717   $95.37   $95.35   $95.40  
  Purchase #2 $99.37   8.296%   $107.6137   $107.61   $107.60   $107.60  
  Purchase #3 $6.25   10.336%   $6.896   $6.90   $6.90   $6.90  
  Purchase #4 $187.36   6.146%   $198.8751   $198.88   $198.90   $198.90  
  Purchase #5 $44.36   12.716%   $50.0008   $50.00   $50.00   $50.00  
  Purchase #6 $176.81   13.127%   $200.0198   $200.02   $200.00   $200.00  
  Purchase #7 $85.43   8.855%   $92.9948   $92.99   $93.00   $93.00  
  7 purchase totals = $684.92       $751.7719   $751.77   $751.75   $751.80