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 $30.76   11.621%   $34.3346   $34.33   $34.35   $34.30  
  Purchase #2 $70.84   8.682%   $76.9903   $76.99   $77.00   $77.00  
  Purchase #3 $175.60   8.599%   $190.6998   $190.70   $190.70   $190.70  
  Purchase #4 $155.93   3.418%   $161.2597   $161.26   $161.25   $161.30  
  Purchase #5 $46.64   7.468%   $50.1231   $50.12   $50.10   $50.10  
  Purchase #6 $98.48   8.163%   $106.5189   $106.52   $106.50   $106.50  
  Purchase #7 $208.62   6.240%   $221.6379   $221.64   $221.65   $221.60  
  7 purchase totals = $786.87       $841.5643   $841.56   $841.55   $841.50