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	$78.90	11.618%	$88.0666	$88.07	$88.05	$88.10
Purchase #2	$109.55	12.381%	$123.1134	$123.11	$123.10	$123.10
Purchase #3	$215.61	12.343%	$242.2227	$242.22	$242.20	$242.20
Purchase #4	$246.84	3.506%	$255.4942	$255.49	$255.50	$255.50
Purchase #5	$152.52	8.368%	$165.2829	$165.28	$165.30	$165.30
Purchase #6	$74.44	5.313%	$78.395	$78.40	$78.40	$78.40
Purchase #7	$81.41	7.332%	$87.379	$87.38	$87.40	$87.40
7 purchase totals =	$959.27		$1,039.9538	$1,039.95	$1,039.95	$1,040.00