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	$17.54	4.432%	$18.3174	$18.32	$18.30	$18.30
Purchase #2	$40.32	8.574%	$43.777	$43.78	$43.80	$43.80
Purchase #3	$136.90	10.460%	$151.2197	$151.22	$151.20	$151.20
Purchase #4	$175.76	11.751%	$196.4136	$196.41	$196.40	$196.40
Purchase #5	$101.52	11.487%	$113.1816	$113.18	$113.20	$113.20
Purchase #6	$40.85	10.705%	$45.223	$45.22	$45.20	$45.20
Purchase #7	$87.35	8.253%	$94.559	$94.56	$94.55	$94.60
7 purchase totals =	$600.24		$662.6913	$662.69	$662.65	$662.70