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 $59.91   6.146%   $63.5921   $63.59   $63.60   $63.60  
  Purchase #2 $218.26   7.186%   $233.9442   $233.94   $233.95   $233.90  
  Purchase #3 $6.89   6.385%   $7.3299   $7.33   $7.35   $7.30  
  Purchase #4 $84.63   3.553%   $87.6369   $87.64   $87.65   $87.60  
  Purchase #5 $36.48   11.806%   $40.7868   $40.79   $40.80   $40.80  
  Purchase #6 $248.59   7.154%   $266.3741   $266.37   $266.35   $266.40  
  Purchase #7 $96.99   3.189%   $100.083   $100.08   $100.10   $100.10  
  7 purchase totals = $751.75       $799.7470   $799.74   $799.80   $799.70