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	$67.81	10.822%	$75.1484	$75.15	$75.15	$75.10
Purchase #2	$21.58	5.555%	$22.7788	$22.78	$22.80	$22.80
Purchase #3	$171.41	10.831%	$189.9754	$189.98	$190.00	$190.00
Purchase #4	$36.75	10.288%	$40.5308	$40.53	$40.55	$40.50
Purchase #5	$37.27	12.530%	$41.9399	$41.94	$41.95	$41.90
Purchase #6	$105.61	6.593%	$112.5729	$112.57	$112.55	$112.60
Purchase #7	$152.54	12.774%	$172.0255	$172.03	$172.05	$172.00
7 purchase totals =	$592.97		$654.9717	$654.98	$655.05	$654.90