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	$43.29	5.569%	$45.7008	$45.70	$45.70	$45.70
Purchase #2	$6.61	4.755%	$6.9243	$6.92	$6.90	$6.90
Purchase #3	$146.47	9.322%	$160.1239	$160.12	$160.10	$160.10
Purchase #4	$140.97	12.337%	$158.3615	$158.36	$158.35	$158.40
Purchase #5	$235.27	6.481%	$250.5178	$250.52	$250.50	$250.50
Purchase #6	$90.97	11.507%	$101.4379	$101.44	$101.45	$101.40
Purchase #7	$83.83	8.447%	$90.9111	$90.91	$90.90	$90.90
7 purchase totals =	$747.41		$813.9773	$813.97	$813.90	$813.90