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	$167.60	8.534%	$181.903	$181.90	$181.90	$181.90
Purchase #2	$223.58	12.632%	$251.8226	$251.82	$251.80	$251.80
Purchase #3	$161.74	6.777%	$172.7011	$172.70	$172.70	$172.70
Purchase #4	$6.54	10.429%	$7.2221	$7.22	$7.20	$7.20
Purchase #5	$54.95	5.248%	$57.8338	$57.83	$57.85	$57.80
Purchase #6	$206.92	7.492%	$222.4224	$222.42	$222.40	$222.40
Purchase #7	$53.42	12.115%	$59.8918	$59.89	$59.90	$59.90
7 purchase totals =	$874.75		$953.7968	$953.78	$953.75	$953.70