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	$50.91	11.255%	$56.6399	$56.64	$56.65	$56.60
Purchase #2	$22.77	7.563%	$24.4921	$24.49	$24.50	$24.50
Purchase #3	$77.75	7.411%	$83.5121	$83.51	$83.50	$83.50
Purchase #4	$131.46	9.355%	$143.7581	$143.76	$143.75	$143.80
Purchase #5	$186.96	4.858%	$196.0425	$196.04	$196.05	$196.00
Purchase #6	$129.36	13.202%	$146.4381	$146.44	$146.45	$146.40
Purchase #7	$180.38	4.309%	$188.1526	$188.15	$188.15	$188.20
7 purchase totals =	$779.59		$839.0354	$839.03	$839.05	$839.00