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 $23.73   11.862%   $26.5449   $26.54   $26.55   $26.50  
  Purchase #2 $155.56   13.249%   $176.1701   $176.17   $176.15   $176.20  
  Purchase #3 $222.56   4.349%   $232.2391   $232.24   $232.25   $232.20  
  Purchase #4 $115.88   5.695%   $122.4794   $122.48   $122.50   $122.50  
  Purchase #5 $196.83   9.503%   $215.5348   $215.53   $215.55   $215.50  
  Purchase #6 $97.79   12.806%   $110.313   $110.31   $110.30   $110.30  
  Purchase #7 $127.97   3.632%   $132.6179   $132.62   $132.60   $132.60  
  7 purchase totals = $940.32       $1,015.8992   $1,015.89   $1,015.90   $1,015.80