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	$114.35	6.218%	$121.4603	$121.46	$121.45	$121.50
Purchase #2	$86.59	5.272%	$91.155	$91.16	$91.15	$91.20
Purchase #3	$45.78	13.206%	$51.8257	$51.83	$51.85	$51.80
Purchase #4	$180.46	3.646%	$187.0396	$187.04	$187.05	$187.00
Purchase #5	$9.80	12.641%	$11.0388	$11.04	$11.05	$11.00
Purchase #6	$14.38	6.730%	$15.3478	$15.35	$15.35	$15.30
Purchase #7	$168.39	10.356%	$185.8285	$185.83	$185.85	$185.80
7 purchase totals =	$619.75		$663.6957	$663.71	$663.75	$663.60