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	$92.51	11.680%	$103.3152	$103.32	$103.30	$103.30
Purchase #2	$22.60	11.570%	$25.2148	$25.21	$25.20	$25.20
Purchase #3	$192.30	9.787%	$211.1204	$211.12	$211.10	$211.10
Purchase #4	$198.52	12.567%	$223.468	$223.47	$223.45	$223.50
Purchase #5	$96.81	4.391%	$101.0609	$101.06	$101.05	$101.10
Purchase #6	$126.72	7.534%	$136.2671	$136.27	$136.25	$136.30
Purchase #7	$162.93	6.452%	$173.4422	$173.44	$173.45	$173.40
7 purchase totals =	$892.39		$973.8886	$973.89	$973.80	$973.90