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 $10.75   12.703%   $12.1156   $12.12   $12.10   $12.10  
  Purchase #2 $123.26   3.543%   $127.6271   $127.63   $127.65   $127.60  
  Purchase #3 $23.99   5.657%   $25.3471   $25.35   $25.35   $25.30  
  Purchase #4 $152.85   6.271%   $162.4352   $162.44   $162.45   $162.40  
  Purchase #5 $165.43   10.334%   $182.5255   $182.53   $182.55   $182.50  
  Purchase #6 $71.38   4.593%   $74.6585   $74.66   $74.65   $74.70  
  Purchase #7 $178.62   7.258%   $191.5842   $191.58   $191.60   $191.60  
  7 purchase totals = $726.28       $776.2932   $776.31   $776.35   $776.20