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	$235.94	13.677%	$268.2095	$268.21	$268.20	$268.20
Purchase #2	$84.70	6.599%	$90.2894	$90.29	$90.30	$90.30
Purchase #3	$200.95	10.848%	$222.7491	$222.75	$222.75	$222.70
Purchase #4	$18.64	4.446%	$19.4687	$19.47	$19.45	$19.50
Purchase #5	$61.49	10.265%	$67.8019	$67.80	$67.80	$67.80
Purchase #6	$25.74	3.175%	$26.5572	$26.56	$26.55	$26.60
Purchase #7	$67.46	5.853%	$71.4084	$71.41	$71.40	$71.40
7 purchase totals =	$694.92		$766.4842	$766.49	$766.45	$766.50