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 $49.39   5.657%   $52.184   $52.18   $52.20   $52.20  
  Purchase #2 $28.91   12.460%   $32.5122   $32.51   $32.50   $32.50  
  Purchase #3 $64.40   5.479%   $67.9285   $67.93   $67.95   $67.90  
  Purchase #4 $241.37   5.350%   $254.2833   $254.28   $254.30   $254.30  
  Purchase #5 $231.77   13.743%   $263.6222   $263.62   $263.60   $263.60  
  Purchase #6 $7.77   6.413%   $8.2683   $8.27   $8.25   $8.30  
  Purchase #7 $34.66   10.319%   $38.2366   $38.24   $38.25   $38.20  
  7 purchase totals = $658.27       $717.0351   $717.03   $717.05   $717.00