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 $168.72   11.212%   $187.6369   $187.64   $187.65   $187.60  
  Purchase #2 $77.90   10.654%   $86.1995   $86.20   $86.20   $86.20  
  Purchase #3 $71.72   10.599%   $79.3216   $79.32   $79.30   $79.30  
  Purchase #4 $236.54   11.482%   $263.6995   $263.70   $263.70   $263.70  
  Purchase #5 $224.66   13.119%   $254.1331   $254.13   $254.15   $254.10  
  Purchase #6 $51.46   5.558%   $54.3201   $54.32   $54.30   $54.30  
  Purchase #7 $41.39   13.430%   $46.9487   $46.95   $46.95   $46.90  
  7 purchase totals = $872.39       $972.2594   $972.26   $972.25   $972.10