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 $213.72   9.310%   $233.6173   $233.62   $233.60   $233.60  
  Purchase #2 $78.41   6.586%   $83.5741   $83.57   $83.55   $83.60  
  Purchase #3 $9.54   3.690%   $9.892   $9.89   $9.90   $9.90  
  Purchase #4 $118.59   6.663%   $126.4917   $126.49   $126.50   $126.50  
  Purchase #5 $106.54   6.629%   $113.6025   $113.60   $113.60   $113.60  
  Purchase #6 $161.70   8.845%   $176.0024   $176.00   $176.00   $176.00  
  Purchase #7 $70.98   7.164%   $76.065   $76.07   $76.05   $76.10  
  7 purchase totals = $759.48       $819.2450   $819.24   $819.20   $819.30