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 $47.36   13.300%   $53.6589   $53.66   $53.65   $53.70  
  Purchase #2 $112.27   5.392%   $118.3236   $118.32   $118.30   $118.30  
  Purchase #3 $81.46   3.720%   $84.4903   $84.49   $84.50   $84.50  
  Purchase #4 $156.94   9.352%   $171.617   $171.62   $171.60   $171.60  
  Purchase #5 $124.51   12.626%   $140.2306   $140.23   $140.25   $140.20  
  Purchase #6 $80.92   4.506%   $84.5663   $84.57   $84.55   $84.60  
  Purchase #7 $100.80   13.103%   $114.0078   $114.01   $114.00   $114.00  
  7 purchase totals = $704.26       $766.8945   $766.90   $766.85   $766.90