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 $23.47   11.652%   $26.2047   $26.20   $26.20   $26.20  
  Purchase #2 $87.67   8.266%   $94.9168   $94.92   $94.90   $94.90  
  Purchase #3 $111.36   10.324%   $122.8568   $122.86   $122.85   $122.90  
  Purchase #4 $71.67   3.613%   $74.2594   $74.26   $74.25   $74.30  
  Purchase #5 $196.51   6.563%   $209.407   $209.41   $209.40   $209.40  
  Purchase #6 $225.97   13.761%   $257.0657   $257.07   $257.05   $257.10  
  Purchase #7 $17.60   4.339%   $18.3637   $18.36   $18.35   $18.40  
  7 purchase totals = $734.25       $803.0741   $803.08   $803.00   $803.20