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 $93.80   4.826%   $98.3268   $98.33   $98.35   $98.30  
  Purchase #2 $6.67   5.798%   $7.0567   $7.06   $7.05   $7.10  
  Purchase #3 $147.54   7.788%   $159.0304   $159.03   $159.05   $159.00  
  Purchase #4 $166.99   6.602%   $178.0147   $178.01   $178.00   $178.00  
  Purchase #5 $246.72   8.296%   $267.1879   $267.19   $267.20   $267.20  
  Purchase #6 $15.66   6.821%   $16.7282   $16.73   $16.75   $16.70  
  Purchase #7 $138.99   5.345%   $146.419   $146.42   $146.40   $146.40  
  7 purchase totals = $816.37       $872.7637   $872.77   $872.80   $872.70