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 $139.62   8.378%   $151.3174   $151.32   $151.30   $151.30  
  Purchase #2 $111.79   9.221%   $122.0982   $122.10   $122.10   $122.10  
  Purchase #3 $234.63   13.349%   $265.9508   $265.95   $265.95   $266.00  
  Purchase #4 $192.84   4.609%   $201.728   $201.73   $201.75   $201.70  
  Purchase #5 $213.77   5.206%   $224.8989   $224.90   $224.90   $224.90  
  Purchase #6 $95.95   3.674%   $99.4752   $99.48   $99.50   $99.50  
  Purchase #7 $158.49   13.495%   $179.8782   $179.88   $179.90   $179.90  
  7 purchase totals = $1,147.09       $1,245.3467   $1,245.36   $1,245.40   $1,245.40