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 $63.28   8.293%   $68.5278   $68.53   $68.55   $68.50  
  Purchase #2 $223.36   3.585%   $231.3675   $231.37   $231.35   $231.40  
  Purchase #3 $91.81   3.797%   $95.296   $95.30   $95.30   $95.30  
  Purchase #4 $209.62   13.227%   $237.3464   $237.35   $237.35   $237.30  
  Purchase #5 $137.74   7.565%   $148.16   $148.16   $148.15   $148.20  
  Purchase #6 $237.72   3.779%   $246.7034   $246.70   $246.70   $246.70  
  Purchase #7 $173.62   13.224%   $196.5795   $196.58   $196.60   $196.60  
  7 purchase totals = $1,137.15       $1,223.9806   $1,223.99   $1,224.00   $1,224.00