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	$189.30	4.867%	$198.5132	$198.51	$198.50	$198.50
Purchase #2	$228.43	6.607%	$243.5224	$243.52	$243.50	$243.50
Purchase #3	$159.41	12.821%	$179.848	$179.85	$179.85	$179.80
Purchase #4	$221.62	10.669%	$245.2646	$245.26	$245.25	$245.30
Purchase #5	$17.50	12.295%	$19.6516	$19.65	$19.65	$19.70
Purchase #6	$132.98	13.636%	$151.1132	$151.11	$151.10	$151.10
Purchase #7	$98.61	13.759%	$112.1777	$112.18	$112.20	$112.20
7 purchase totals =	$1,047.85		$1,150.0907	$1,150.08	$1,150.05	$1,150.10