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 $133.28   5.403%   $140.4811   $140.48   $140.50   $140.50  
  Purchase #2 $15.70   5.310%   $16.5337   $16.53   $16.55   $16.50  
  Purchase #3 $9.28   6.268%   $9.8617   $9.86   $9.85   $9.90  
  Purchase #4 $107.88   13.367%   $122.3003   $122.30   $122.30   $122.30  
  Purchase #5 $62.50   6.390%   $66.4938   $66.49   $66.50   $66.50  
  Purchase #6 $51.43   7.278%   $55.1731   $55.17   $55.15   $55.20  
  Purchase #7 $174.46   12.798%   $196.7874   $196.79   $196.80   $196.80  
  7 purchase totals = $554.53       $607.6311   $607.62   $607.65   $607.70