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 $95.28   3.834%   $98.933   $98.93   $98.95   $98.90  
  Purchase #2 $33.48   5.233%   $35.232   $35.23   $35.25   $35.20  
  Purchase #3 $134.83   8.286%   $146.002   $146.00   $146.00   $146.00  
  Purchase #4 $120.99   3.625%   $125.3759   $125.38   $125.40   $125.40  
  Purchase #5 $115.26   6.286%   $122.5052   $122.51   $122.50   $122.50  
  Purchase #6 $17.56   8.409%   $19.0366   $19.04   $19.05   $19.00  
  Purchase #7 $238.33   11.129%   $264.8537   $264.85   $264.85   $264.90  
  7 purchase totals = $755.73       $811.9384   $811.94   $812.00   $811.90