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 $244.73   8.722%   $266.0754   $266.08   $266.10   $266.10  
  Purchase #2 $130.75   9.323%   $142.9398   $142.94   $142.95   $142.90  
  Purchase #3 $83.62   13.525%   $94.9296   $94.93   $94.95   $94.90  
  Purchase #4 $143.39   8.603%   $155.7258   $155.73   $155.75   $155.70  
  Purchase #5 $107.71   5.231%   $113.3443   $113.34   $113.35   $113.30  
  Purchase #6 $91.35   7.468%   $98.172   $98.17   $98.15   $98.20  
  Purchase #7 $130.77   3.673%   $135.5732   $135.57   $135.55   $135.60  
  7 purchase totals = $932.32       $1,006.7601   $1,006.76   $1,006.80   $1,006.70