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	$78.78	13.814%	$89.6627	$89.66	$89.65	$89.70
Purchase #2	$61.86	10.665%	$68.4574	$68.46	$68.45	$68.50
Purchase #3	$162.49	3.627%	$168.3835	$168.38	$168.40	$168.40
Purchase #4	$181.30	5.411%	$191.1101	$191.11	$191.10	$191.10
Purchase #5	$158.81	7.255%	$170.3317	$170.33	$170.35	$170.30
Purchase #6	$89.52	13.212%	$101.3474	$101.35	$101.35	$101.30
Purchase #7	$213.84	11.324%	$238.0552	$238.06	$238.05	$238.10
7 purchase totals =	$946.60		$1,027.3480	$1,027.35	$1,027.35	$1,027.40