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	$185.56	9.138%	$202.5165	$202.52	$202.50	$202.50
Purchase #2	$203.82	12.685%	$229.6746	$229.67	$229.65	$229.70
Purchase #3	$87.71	12.664%	$98.8176	$98.82	$98.80	$98.80
Purchase #4	$89.71	12.484%	$100.9094	$100.91	$100.90	$100.90
Purchase #5	$145.89	8.481%	$158.2629	$158.26	$158.25	$158.30
Purchase #6	$96.94	11.125%	$107.7246	$107.72	$107.70	$107.70
Purchase #7	$109.61	4.571%	$114.6203	$114.62	$114.60	$114.60
7 purchase totals =	$919.24		$1,012.5259	$1,012.52	$1,012.40	$1,012.50