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 $59.61   11.581%   $66.5134   $66.51   $66.50   $66.50  
  Purchase #2 $115.61   7.339%   $124.0946   $124.09   $124.10   $124.10  
  Purchase #3 $159.89   10.434%   $176.5729   $176.57   $176.55   $176.60  
  Purchase #4 $176.44   8.828%   $192.0161   $192.02   $192.00   $192.00  
  Purchase #5 $13.29   8.269%   $14.389   $14.39   $14.40   $14.40  
  Purchase #6 $177.66   6.357%   $188.9538   $188.95   $188.95   $189.00  
  Purchase #7 $179.64   5.537%   $189.5867   $189.59   $189.60   $189.60  
  7 purchase totals = $882.14       $952.1265   $952.12   $952.10   $952.20