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	$38.33	13.356%	$43.4494	$43.45	$43.45	$43.40
Purchase #2	$13.67	3.220%	$14.1102	$14.11	$14.10	$14.10
Purchase #3	$185.49	3.378%	$191.7559	$191.76	$191.75	$191.80
Purchase #4	$199.78	11.280%	$222.3152	$222.32	$222.30	$222.30
Purchase #5	$144.31	8.593%	$156.7106	$156.71	$156.70	$156.70
Purchase #6	$26.95	4.163%	$28.0719	$28.07	$28.05	$28.10
Purchase #7	$199.86	6.188%	$212.2273	$212.23	$212.25	$212.20
7 purchase totals =	$808.39		$868.6405	$868.65	$868.60	$868.60