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 $93.71   5.337%   $98.7113   $98.71   $98.70   $98.70  
  Purchase #2 $85.41   8.602%   $92.757   $92.76   $92.75   $92.80  
  Purchase #3 $194.61   4.657%   $203.673   $203.67   $203.65   $203.70  
  Purchase #4 $104.89   9.218%   $114.5588   $114.56   $114.55   $114.60  
  Purchase #5 $58.35   6.247%   $61.9951   $62.00   $62.00   $62.00  
  Purchase #6 $161.77   8.806%   $176.0155   $176.02   $176.00   $176.00  
  Purchase #7 $245.67   5.364%   $258.8477   $258.85   $258.85   $258.80  
  7 purchase totals = $944.41       $1,006.5584   $1,006.57   $1,006.50   $1,006.60