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	$70.32	10.577%	$77.7577	$77.76	$77.75	$77.80
Purchase #2	$159.88	9.251%	$174.6705	$174.67	$174.65	$174.70
Purchase #3	$230.61	4.525%	$241.0451	$241.05	$241.05	$241.00
Purchase #4	$162.52	12.410%	$182.6887	$182.69	$182.70	$182.70
Purchase #5	$99.75	6.165%	$105.8996	$105.90	$105.90	$105.90
Purchase #6	$166.45	11.418%	$185.4553	$185.46	$185.45	$185.50
Purchase #7	$151.76	13.227%	$171.8333	$171.83	$171.85	$171.80
7 purchase totals =	$1,041.29		$1,139.3502	$1,139.36	$1,139.35	$1,139.40