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 $241.88   8.526%   $262.5027   $262.50   $262.50   $262.50  
  Purchase #2 $5.85   3.108%   $6.0318   $6.03   $6.05   $6.00  
  Purchase #3 $218.90   8.679%   $237.8983   $237.90   $237.90   $237.90  
  Purchase #4 $67.52   9.346%   $73.8304   $73.83   $73.85   $73.80  
  Purchase #5 $85.50   3.794%   $88.7439   $88.74   $88.75   $88.70  
  Purchase #6 $207.57   7.512%   $223.1627   $223.16   $223.15   $223.20  
  Purchase #7 $241.79   13.553%   $274.5598   $274.56   $274.55   $274.60  
  7 purchase totals = $1,069.01       $1,166.7296   $1,166.72   $1,166.75   $1,166.70