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 $246.64   8.162%   $266.7708   $266.77   $266.75   $266.80  
  Purchase #2 $146.90   7.697%   $158.2069   $158.21   $158.20   $158.20  
  Purchase #3 $210.34   5.410%   $221.7194   $221.72   $221.70   $221.70  
  Purchase #4 $12.31   3.147%   $12.6974   $12.70   $12.70   $12.70  
  Purchase #5 $229.56   8.632%   $249.3756   $249.38   $249.40   $249.40  
  Purchase #6 $91.59   9.393%   $100.193   $100.19   $100.20   $100.20  
  Purchase #7 $21.74   11.821%   $24.3099   $24.31   $24.30   $24.30  
  7 purchase totals = $959.08       $1,033.2730   $1,033.28   $1,033.25   $1,033.30