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 $243.91   12.836%   $275.2183   $275.22   $275.20   $275.20  
  Purchase #2 $72.88   6.102%   $77.3271   $77.33   $77.35   $77.30  
  Purchase #3 $223.69   4.722%   $234.2526   $234.25   $234.25   $234.30  
  Purchase #4 $101.49   11.701%   $113.3653   $113.37   $113.35   $113.40  
  Purchase #5 $168.45   4.849%   $176.6181   $176.62   $176.60   $176.60  
  Purchase #6 $144.91   8.534%   $157.2766   $157.28   $157.30   $157.30  
  Purchase #7 $112.40   10.838%   $124.5819   $124.58   $124.60   $124.60  
  7 purchase totals = $1,067.73       $1,158.6399   $1,158.65   $1,158.65   $1,158.70