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 $73.50   11.773%   $82.1532   $82.15   $82.15   $82.20  
  Purchase #2 $174.70   4.627%   $182.7834   $182.78   $182.80   $182.80  
  Purchase #3 $224.34   3.616%   $232.4521   $232.45   $232.45   $232.50  
  Purchase #4 $111.99   10.180%   $123.3906   $123.39   $123.40   $123.40  
  Purchase #5 $206.69   10.473%   $228.3366   $228.34   $228.35   $228.30  
  Purchase #6 $116.99   10.394%   $129.1499   $129.15   $129.15   $129.10  
  Purchase #7 $42.88   13.112%   $48.5024   $48.50   $48.50   $48.50  
  7 purchase totals = $951.09       $1,026.7682   $1,026.76   $1,026.80   $1,026.80