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	$71.28	9.407%	$77.9853	$77.99	$78.00	$78.00
Purchase #2	$235.56	3.445%	$243.675	$243.68	$243.70	$243.70
Purchase #3	$148.28	12.759%	$167.199	$167.20	$167.20	$167.20
Purchase #4	$172.95	4.103%	$180.0461	$180.05	$180.05	$180.00
Purchase #5	$95.40	9.580%	$104.5393	$104.54	$104.55	$104.50
Purchase #6	$179.40	3.307%	$185.3328	$185.33	$185.35	$185.30
Purchase #7	$153.28	12.707%	$172.7573	$172.76	$172.75	$172.80
7 purchase totals =	$1,056.15		$1,131.5348	$1,131.55	$1,131.60	$1,131.50