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	$13.29	13.272%	$15.0538	$15.05	$15.05	$15.10
Purchase #2	$9.39	12.454%	$10.5594	$10.56	$10.55	$10.60
Purchase #3	$124.49	9.872%	$136.7797	$136.78	$136.80	$136.80
Purchase #4	$68.90	5.851%	$72.9313	$72.93	$72.95	$72.90
Purchase #5	$91.66	4.395%	$95.6885	$95.69	$95.70	$95.70
Purchase #6	$33.96	12.308%	$38.1398	$38.14	$38.15	$38.10
Purchase #7	$250.76	9.818%	$275.3796	$275.38	$275.40	$275.40
7 purchase totals =	$592.45		$644.5321	$644.53	$644.60	$644.60