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 $221.77   4.144%   $230.9601   $230.96   $230.95   $231.00  
  Purchase #2 $200.55   8.159%   $216.9129   $216.91   $216.90   $216.90  
  Purchase #3 $187.85   7.799%   $202.5004   $202.50   $202.50   $202.50  
  Purchase #4 $76.73   7.795%   $82.7111   $82.71   $82.70   $82.70  
  Purchase #5 $149.65   3.485%   $154.8653   $154.87   $154.85   $154.90  
  Purchase #6 $179.37   11.324%   $199.6819   $199.68   $199.70   $199.70  
  Purchase #7 $188.86   9.461%   $206.728   $206.73   $206.75   $206.70  
  7 purchase totals = $1,204.78       $1,294.3597   $1,294.36   $1,294.35   $1,294.40