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 $59.26   10.191%   $65.2992   $65.30   $65.30   $65.30  
  Purchase #2 $19.95   13.601%   $22.6634   $22.66   $22.65   $22.70  
  Purchase #3 $122.73   5.822%   $129.8753   $129.88   $129.90   $129.90  
  Purchase #4 $80.42   4.563%   $84.0896   $84.09   $84.10   $84.10  
  Purchase #5 $18.78   4.713%   $19.6651   $19.67   $19.65   $19.70  
  Purchase #6 $104.32   10.508%   $115.2819   $115.28   $115.30   $115.30  
  Purchase #7 $249.49   11.230%   $277.5077   $277.51   $277.50   $277.50  
  7 purchase totals = $654.95       $714.3822   $714.39   $714.40   $714.50