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 $88.91   3.422%   $91.9525   $91.95   $91.95   $92.00  
  Purchase #2 $13.29   6.271%   $14.1234   $14.12   $14.10   $14.10  
  Purchase #3 $105.87   12.860%   $119.4849   $119.48   $119.50   $119.50  
  Purchase #4 $163.96   8.355%   $177.6589   $177.66   $177.65   $177.70  
  Purchase #5 $149.28   8.647%   $162.1882   $162.19   $162.20   $162.20  
  Purchase #6 $107.81   11.343%   $120.0389   $120.04   $120.05   $120.00  
  Purchase #7 $52.60   12.113%   $58.9714   $58.97   $58.95   $59.00  
  7 purchase totals = $681.72       $744.4182   $744.41   $744.40   $744.50