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	$21.31	3.514%	$22.0588	$22.06	$22.05	$22.10
Purchase #2	$98.73	13.751%	$112.3064	$112.31	$112.30	$112.30
Purchase #3	$104.91	4.609%	$109.7453	$109.75	$109.75	$109.70
Purchase #4	$67.33	4.248%	$70.1902	$70.19	$70.20	$70.20
Purchase #5	$85.77	6.607%	$91.4368	$91.44	$91.45	$91.40
Purchase #6	$67.99	4.671%	$71.1658	$71.17	$71.15	$71.20
Purchase #7	$153.61	12.757%	$173.206	$173.21	$173.20	$173.20
7 purchase totals =	$599.65		$650.1093	$650.13	$650.10	$650.10