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	$102.47	6.362%	$108.9891	$108.99	$109.00	$109.00
Purchase #2	$119.72	3.392%	$123.7809	$123.78	$123.80	$123.80
Purchase #3	$53.85	13.383%	$61.0567	$61.06	$61.05	$61.10
Purchase #4	$6.94	10.196%	$7.6476	$7.65	$7.65	$7.60
Purchase #5	$89.74	12.202%	$100.6901	$100.69	$100.70	$100.70
Purchase #6	$127.73	4.656%	$133.6771	$133.68	$133.70	$133.70
Purchase #7	$191.27	6.371%	$203.4558	$203.46	$203.45	$203.50
7 purchase totals =	$691.72		$739.2973	$739.31	$739.35	$739.40