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	$214.72	3.521%	$222.2803	$222.28	$222.30	$222.30
Purchase #2	$112.86	13.700%	$128.3218	$128.32	$128.30	$128.30
Purchase #3	$151.76	8.675%	$164.9252	$164.93	$164.95	$164.90
Purchase #4	$124.47	3.388%	$128.687	$128.69	$128.70	$128.70
Purchase #5	$216.27	5.212%	$227.542	$227.54	$227.55	$227.50
Purchase #6	$73.26	8.220%	$79.282	$79.28	$79.30	$79.30
Purchase #7	$79.97	10.556%	$88.4116	$88.41	$88.40	$88.40
7 purchase totals =	$973.31		$1,039.4499	$1,039.45	$1,039.50	$1,039.40