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	$115.55	11.504%	$128.8429	$128.84	$128.85	$128.80
Purchase #2	$94.46	6.336%	$100.445	$100.45	$100.45	$100.40
Purchase #3	$132.97	13.578%	$151.0247	$151.02	$151.00	$151.00
Purchase #4	$52.56	4.763%	$55.0634	$55.06	$55.05	$55.10
Purchase #5	$175.88	9.432%	$192.469	$192.47	$192.45	$192.50
Purchase #6	$53.30	13.516%	$60.504	$60.50	$60.50	$60.50
Purchase #7	$155.44	9.444%	$170.1198	$170.12	$170.10	$170.10
7 purchase totals =	$780.16		$858.4688	$858.46	$858.40	$858.40