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 $49.59   13.211%   $56.1413   $56.14   $56.15   $56.10  
  Purchase #2 $86.71   9.663%   $95.0888   $95.09   $95.10   $95.10  
  Purchase #3 $176.83   8.232%   $191.3866   $191.39   $191.40   $191.40  
  Purchase #4 $70.90   11.577%   $79.1081   $79.11   $79.10   $79.10  
  Purchase #5 $100.64   6.334%   $107.0145   $107.01   $107.00   $107.00  
  Purchase #6 $68.73   9.137%   $75.0099   $75.01   $75.00   $75.00  
  Purchase #7 $146.67   4.214%   $152.8507   $152.85   $152.85   $152.90  
  7 purchase totals = $700.07       $756.5999   $756.60   $756.60   $756.60