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	$214.30	6.839%	$228.956	$228.96	$228.95	$229.00
Purchase #2	$92.32	10.362%	$101.8862	$101.89	$101.90	$101.90
Purchase #3	$101.40	9.731%	$111.2672	$111.27	$111.25	$111.30
Purchase #4	$92.25	13.727%	$104.9132	$104.91	$104.90	$104.90
Purchase #5	$6.36	7.358%	$6.828	$6.83	$6.85	$6.80
Purchase #6	$82.69	4.632%	$86.5202	$86.52	$86.50	$86.50
Purchase #7	$54.37	9.839%	$59.7195	$59.72	$59.70	$59.70
7 purchase totals =	$643.69		$700.0903	$700.10	$700.05	$700.10