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	$86.52	13.829%	$98.4849	$98.48	$98.50	$98.50
Purchase #2	$236.62	7.538%	$254.4564	$254.46	$254.45	$254.50
Purchase #3	$13.74	3.525%	$14.2243	$14.22	$14.20	$14.20
Purchase #4	$40.25	7.198%	$43.1472	$43.15	$43.15	$43.10
Purchase #5	$106.94	7.425%	$114.8803	$114.88	$114.90	$114.90
Purchase #6	$88.83	11.519%	$99.0623	$99.06	$99.05	$99.10
Purchase #7	$12.25	7.803%	$13.2059	$13.21	$13.20	$13.20
7 purchase totals =	$585.15		$637.4613	$637.46	$637.45	$637.50