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 $38.45   12.852%   $43.3916   $43.39   $43.40   $43.40  
  Purchase #2 $56.32   12.263%   $63.2265   $63.23   $63.25   $63.20  
  Purchase #3 $200.74   3.114%   $206.991   $206.99   $207.00   $207.00  
  Purchase #4 $25.29   4.149%   $26.3393   $26.34   $26.35   $26.30  
  Purchase #5 $103.76   12.298%   $116.5204   $116.52   $116.50   $116.50  
  Purchase #6 $218.47   3.403%   $225.9045   $225.90   $225.90   $225.90  
  Purchase #7 $15.75   3.124%   $16.242   $16.24   $16.25   $16.20  
  7 purchase totals = $658.78       $698.6153   $698.61   $698.65   $698.50