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 $209.72   11.218%   $233.2464   $233.25   $233.25   $233.20  
  Purchase #2 $32.76   4.237%   $34.148   $34.15   $34.15   $34.10  
  Purchase #3 $45.99   3.703%   $47.693   $47.69   $47.70   $47.70  
  Purchase #4 $106.25   8.386%   $115.1601   $115.16   $115.15   $115.20  
  Purchase #5 $89.50   12.292%   $100.5013   $100.50   $100.50   $100.50  
  Purchase #6 $23.26   3.122%   $23.9862   $23.99   $24.00   $24.00  
  Purchase #7 $213.93   9.849%   $235   $235.00   $235.00   $235.00  
  7 purchase totals = $721.41       $789.7350   $789.74   $789.75   $789.70