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 $153.27   13.216%   $173.5262   $173.53   $173.55   $173.50  
  Purchase #2 $71.57   7.346%   $76.8275   $76.83   $76.85   $76.80  
  Purchase #3 $239.56   11.332%   $266.7069   $266.71   $266.70   $266.70  
  Purchase #4 $152.83   8.324%   $165.5516   $165.55   $165.55   $165.60  
  Purchase #5 $239.57   4.506%   $250.365   $250.37   $250.35   $250.40  
  Purchase #6 $74.31   9.174%   $81.1272   $81.13   $81.15   $81.10  
  Purchase #7 $229.90   5.333%   $242.1606   $242.16   $242.15   $242.20  
  7 purchase totals = $1,161.01       $1,256.2650   $1,256.28   $1,256.30   $1,256.30