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 $188.95   6.384%   $201.0126   $201.01   $201.00   $201.00  
  Purchase #2 $62.91   4.598%   $65.8026   $65.80   $65.80   $65.80  
  Purchase #3 $71.69   3.840%   $74.4429   $74.44   $74.45   $74.40  
  Purchase #4 $137.36   12.673%   $154.7676   $154.77   $154.75   $154.80  
  Purchase #5 $71.41   3.609%   $73.9872   $73.99   $74.00   $74.00  
  Purchase #6 $46.98   11.400%   $52.3357   $52.34   $52.35   $52.30  
  Purchase #7 $240.35   13.458%   $272.6963   $272.70   $272.70   $272.70  
  7 purchase totals = $819.65       $895.0449   $895.05   $895.05   $895.00