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	$106.69	12.370%	$119.8876	$119.89	$119.90	$119.90
Purchase #2	$125.68	6.663%	$134.0541	$134.05	$134.05	$134.10
Purchase #3	$85.99	3.753%	$89.2172	$89.22	$89.20	$89.20
Purchase #4	$70.48	11.745%	$78.7579	$78.76	$78.75	$78.80
Purchase #5	$136.35	3.493%	$141.1127	$141.11	$141.10	$141.10
Purchase #6	$20.65	13.150%	$23.3655	$23.37	$23.35	$23.40
Purchase #7	$154.37	5.229%	$162.442	$162.44	$162.45	$162.40
7 purchase totals =	$700.21		$748.8370	$748.84	$748.80	$748.90