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	$245.51	3.195%	$253.354	$253.35	$253.35	$253.40
Purchase #2	$161.33	6.665%	$172.0826	$172.08	$172.10	$172.10
Purchase #3	$147.52	11.484%	$164.4612	$164.46	$164.45	$164.50
Purchase #4	$66.63	7.793%	$71.8225	$71.82	$71.80	$71.80
Purchase #5	$75.35	6.530%	$80.2704	$80.27	$80.25	$80.30
Purchase #6	$40.26	3.233%	$41.5616	$41.56	$41.55	$41.60
Purchase #7	$18.95	9.824%	$20.8116	$20.81	$20.80	$20.80
7 purchase totals =	$755.55		$804.3639	$804.35	$804.30	$804.50