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	$179.70	11.333%	$200.0654	$200.07	$200.05	$200.10
Purchase #2	$231.76	8.175%	$250.7064	$250.71	$250.70	$250.70
Purchase #3	$121.66	12.206%	$136.5098	$136.51	$136.50	$136.50
Purchase #4	$110.63	9.786%	$121.4563	$121.46	$121.45	$121.50
Purchase #5	$166.89	11.220%	$185.6151	$185.62	$185.60	$185.60
Purchase #6	$35.97	11.840%	$40.2288	$40.23	$40.25	$40.20
Purchase #7	$89.54	13.848%	$101.9395	$101.94	$101.95	$101.90
7 purchase totals =	$936.15		$1,036.5213	$1,036.54	$1,036.50	$1,036.50