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	$19.75	5.407%	$20.8179	$20.82	$20.80	$20.80
Purchase #2	$5.45	12.259%	$6.1181	$6.12	$6.10	$6.10
Purchase #3	$152.31	3.825%	$158.1359	$158.14	$158.15	$158.10
Purchase #4	$174.87	9.304%	$191.1399	$191.14	$191.15	$191.10
Purchase #5	$199.94	11.614%	$223.161	$223.16	$223.15	$223.20
Purchase #6	$222.57	10.174%	$245.2143	$245.21	$245.20	$245.20
Purchase #7	$97.61	5.582%	$103.0586	$103.06	$103.05	$103.10
7 purchase totals =	$872.50		$947.6457	$947.65	$947.60	$947.60