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	$35.38	10.223%	$38.9969	$39.00	$39.00	$39.00
Purchase #2	$175.45	11.869%	$196.2742	$196.27	$196.25	$196.30
Purchase #3	$111.62	13.702%	$126.9142	$126.91	$126.90	$126.90
Purchase #4	$11.90	3.263%	$12.2883	$12.29	$12.30	$12.30
Purchase #5	$25.62	12.265%	$28.7623	$28.76	$28.75	$28.80
Purchase #6	$191.82	3.383%	$198.3093	$198.31	$198.30	$198.30
Purchase #7	$30.44	10.586%	$33.6624	$33.66	$33.65	$33.70
7 purchase totals =	$582.23		$635.2076	$635.20	$635.15	$635.30