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	$190.46	13.128%	$215.4636	$215.46	$215.45	$215.50
Purchase #2	$172.58	12.626%	$194.37	$194.37	$194.35	$194.40
Purchase #3	$71.75	12.463%	$80.6922	$80.69	$80.70	$80.70
Purchase #4	$143.65	13.106%	$162.4768	$162.48	$162.50	$162.50
Purchase #5	$67.91	7.367%	$72.9129	$72.91	$72.90	$72.90
Purchase #6	$154.76	7.734%	$166.7291	$166.73	$166.75	$166.70
Purchase #7	$25.64	8.665%	$27.8617	$27.86	$27.85	$27.90
7 purchase totals =	$826.75		$920.5063	$920.50	$920.50	$920.60