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 $87.28   12.657%   $98.327   $98.33   $98.35   $98.30  
  Purchase #2 $7.58   5.510%   $7.9977   $8.00   $8.00   $8.00  
  Purchase #3 $191.67   11.837%   $214.358   $214.36   $214.35   $214.40  
  Purchase #4 $192.33   10.143%   $211.838   $211.84   $211.85   $211.80  
  Purchase #5 $189.41   4.795%   $198.4922   $198.49   $198.50   $198.50  
  Purchase #6 $114.43   6.860%   $122.2799   $122.28   $122.30   $122.30  
  Purchase #7 $36.36   11.669%   $40.6028   $40.60   $40.60   $40.60  
  7 purchase totals = $819.06       $893.8956   $893.90   $893.95   $893.90