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 $182.40   8.295%   $197.5301   $197.53   $197.55   $197.50  
  Purchase #2 $123.69   9.375%   $135.2859   $135.29   $135.30   $135.30  
  Purchase #3 $238.52   11.419%   $265.7566   $265.76   $265.75   $265.80  
  Purchase #4 $94.45   4.535%   $98.7333   $98.73   $98.75   $98.70  
  Purchase #5 $94.76   11.558%   $105.7124   $105.71   $105.70   $105.70  
  Purchase #6 $176.61   12.236%   $198.22   $198.22   $198.20   $198.20  
  Purchase #7 $53.35   7.639%   $57.4254   $57.43   $57.45   $57.40  
  7 purchase totals = $963.78       $1,058.6637   $1,058.67   $1,058.70   $1,058.60