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 $68.70   9.158%   $74.9915   $74.99   $75.00   $75.00  
  Purchase #2 $221.37   4.751%   $231.8873   $231.89   $231.90   $231.90  
  Purchase #3 $25.33   6.506%   $26.978   $26.98   $27.00   $27.00  
  Purchase #4 $116.91   6.271%   $124.2414   $124.24   $124.25   $124.20  
  Purchase #5 $13.39   11.158%   $14.8841   $14.88   $14.90   $14.90  
  Purchase #6 $151.62   6.865%   $162.0287   $162.03   $162.05   $162.00  
  Purchase #7 $69.68   13.226%   $78.8959   $78.90   $78.90   $78.90  
  7 purchase totals = $667.00       $713.9069   $713.91   $714.00   $713.90