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	$225.92	13.246%	$255.8454	$255.85	$255.85	$255.80
Purchase #2	$212.97	11.817%	$238.1367	$238.14	$238.15	$238.10
Purchase #3	$161.29	6.179%	$171.2561	$171.26	$171.25	$171.30
Purchase #4	$138.33	5.437%	$145.851	$145.85	$145.85	$145.90
Purchase #5	$115.75	11.488%	$129.0474	$129.05	$129.05	$129.00
Purchase #6	$34.73	7.825%	$37.4476	$37.45	$37.45	$37.40
Purchase #7	$209.32	6.246%	$222.3941	$222.39	$222.40	$222.40
7 purchase totals =	$1,098.31		$1,199.9783	$1,199.99	$1,200.00	$1,199.90