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 $84.48   7.371%   $90.707   $90.71   $90.70   $90.70  
  Purchase #2 $6.53   7.778%   $7.0379   $7.04   $7.05   $7.00  
  Purchase #3 $15.77   13.154%   $17.8444   $17.84   $17.85   $17.80  
  Purchase #4 $191.48   3.433%   $198.0535   $198.05   $198.05   $198.10  
  Purchase #5 $15.93   12.495%   $17.9205   $17.92   $17.90   $17.90  
  Purchase #6 $100.59   8.540%   $109.1804   $109.18   $109.20   $109.20  
  Purchase #7 $5.91   11.605%   $6.5959   $6.60   $6.60   $6.60  
  7 purchase totals = $420.69       $447.3396   $447.34   $447.35   $447.30