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	$100.69	7.317%	$108.0575	$108.06	$108.05	$108.10
Purchase #2	$59.45	5.449%	$62.6894	$62.69	$62.70	$62.70
Purchase #3	$116.27	12.790%	$131.1409	$131.14	$131.15	$131.10
Purchase #4	$37.68	7.481%	$40.4988	$40.50	$40.50	$40.50
Purchase #5	$147.88	4.576%	$154.647	$154.65	$154.65	$154.60
Purchase #6	$137.48	12.410%	$154.5413	$154.54	$154.55	$154.50
Purchase #7	$155.54	10.315%	$171.584	$171.58	$171.60	$171.60
7 purchase totals =	$754.99		$823.1589	$823.16	$823.20	$823.10