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	$199.28	11.572%	$222.3407	$222.34	$222.35	$222.30
Purchase #2	$159.81	13.188%	$180.8857	$180.89	$180.90	$180.90
Purchase #3	$219.75	4.649%	$229.9662	$229.97	$229.95	$230.00
Purchase #4	$207.89	7.765%	$224.0327	$224.03	$224.05	$224.00
Purchase #5	$78.65	8.594%	$85.4092	$85.41	$85.40	$85.40
Purchase #6	$73.68	11.874%	$82.4288	$82.43	$82.45	$82.40
Purchase #7	$231.72	10.204%	$255.3647	$255.36	$255.35	$255.40
7 purchase totals =	$1,170.78		$1,280.4280	$1,280.43	$1,280.45	$1,280.40