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 $232.34   13.140%   $262.8695   $262.87   $262.85   $262.90  
  Purchase #2 $123.42   11.468%   $137.5738   $137.57   $137.55   $137.60  
  Purchase #3 $35.79   8.387%   $38.7917   $38.79   $38.80   $38.80  
  Purchase #4 $81.97   11.676%   $91.5408   $91.54   $91.55   $91.50  
  Purchase #5 $170.27   4.252%   $177.5099   $177.51   $177.50   $177.50  
  Purchase #6 $70.90   6.757%   $75.6907   $75.69   $75.70   $75.70  
  Purchase #7 $162.98   11.666%   $181.9932   $181.99   $182.00   $182.00  
  7 purchase totals = $877.67       $965.9696   $965.96   $965.95   $966.00