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 $63.29   6.666%   $67.5089   $67.51   $67.50   $67.50  
  Purchase #2 $206.99   4.762%   $216.8469   $216.85   $216.85   $216.80  
  Purchase #3 $94.42   6.873%   $100.9095   $100.91   $100.90   $100.90  
  Purchase #4 $201.73   9.634%   $221.1647   $221.16   $221.15   $221.20  
  Purchase #5 $119.41   3.750%   $123.8879   $123.89   $123.90   $123.90  
  Purchase #6 $238.57   4.368%   $248.9907   $248.99   $249.00   $249.00  
  Purchase #7 $112.74   5.864%   $119.3511   $119.35   $119.35   $119.40  
  7 purchase totals = $1,037.15       $1,098.6597   $1,098.66   $1,098.65   $1,098.70