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	$212.37	4.275%	$221.4488	$221.45	$221.45	$221.40
Purchase #2	$25.54	6.497%	$27.1993	$27.20	$27.20	$27.20
Purchase #3	$75.55	3.388%	$78.1096	$78.11	$78.10	$78.10
Purchase #4	$45.39	6.123%	$48.1692	$48.17	$48.15	$48.20
Purchase #5	$123.77	3.481%	$128.0784	$128.08	$128.10	$128.10
Purchase #6	$75.27	7.145%	$80.648	$80.65	$80.65	$80.60
Purchase #7	$244.55	4.649%	$255.9191	$255.92	$255.90	$255.90
7 purchase totals =	$802.44		$839.5724	$839.58	$839.55	$839.50