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 $242.99   13.682%   $276.2359   $276.24   $276.25   $276.20  
  Purchase #2 $65.87   11.707%   $73.5814   $73.58   $73.60   $73.60  
  Purchase #3 $230.52   6.265%   $244.9621   $244.96   $244.95   $245.00  
  Purchase #4 $139.99   11.247%   $155.7347   $155.73   $155.75   $155.70  
  Purchase #5 $40.95   12.326%   $45.9975   $46.00   $46.00   $46.00  
  Purchase #6 $98.95   6.652%   $105.5322   $105.53   $105.55   $105.50  
  Purchase #7 $131.97   3.839%   $137.0363   $137.04   $137.05   $137.00  
  7 purchase totals = $951.24       $1,039.0801   $1,039.08   $1,039.15   $1,039.00