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	$213.72	4.290%	$222.8886	$222.89	$222.90	$222.90
Purchase #2	$50.26	5.467%	$53.0077	$53.01	$53.00	$53.00
Purchase #3	$249.37	13.605%	$283.2968	$283.30	$283.30	$283.30
Purchase #4	$167.49	10.597%	$185.2389	$185.24	$185.25	$185.20
Purchase #5	$6.71	10.851%	$7.4381	$7.44	$7.45	$7.40
Purchase #6	$191.26	12.483%	$215.135	$215.14	$215.15	$215.10
Purchase #7	$12.39	7.114%	$13.2714	$13.27	$13.25	$13.30
7 purchase totals =	$891.20		$980.2765	$980.29	$980.30	$980.20