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	$173.72	6.136%	$184.3795	$184.38	$184.40	$184.40
Purchase #2	$35.30	5.492%	$37.2387	$37.24	$37.25	$37.20
Purchase #3	$177.73	12.699%	$200.2999	$200.30	$200.30	$200.30
Purchase #4	$182.75	3.716%	$189.541	$189.54	$189.55	$189.50
Purchase #5	$50.37	9.500%	$55.1552	$55.16	$55.15	$55.20
Purchase #6	$86.27	5.359%	$90.8932	$90.89	$90.90	$90.90
Purchase #7	$77.96	7.732%	$83.9879	$83.99	$84.00	$84.00
7 purchase totals =	$784.10		$841.4954	$841.50	$841.55	$841.50