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	$231.89	13.135%	$262.3488	$262.35	$262.35	$262.30
Purchase #2	$223.86	6.734%	$238.9347	$238.93	$238.95	$238.90
Purchase #3	$231.56	3.582%	$239.8545	$239.85	$239.85	$239.90
Purchase #4	$91.60	6.754%	$97.7867	$97.79	$97.80	$97.80
Purchase #5	$107.70	3.324%	$111.2799	$111.28	$111.30	$111.30
Purchase #6	$51.76	5.498%	$54.6058	$54.61	$54.60	$54.60
Purchase #7	$62.33	13.156%	$70.5301	$70.53	$70.55	$70.50
7 purchase totals =	$1,000.70		$1,075.3405	$1,075.34	$1,075.40	$1,075.30