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	$161.73	10.401%	$178.5515	$178.55	$178.55	$178.60
Purchase #2	$144.84	4.149%	$150.8494	$150.85	$150.85	$150.80
Purchase #3	$112.78	4.842%	$118.2408	$118.24	$118.25	$118.20
Purchase #4	$209.89	13.172%	$237.5367	$237.54	$237.55	$237.50
Purchase #5	$80.52	13.322%	$91.2469	$91.25	$91.25	$91.20
Purchase #6	$107.57	6.335%	$114.3846	$114.38	$114.40	$114.40
Purchase #7	$82.92	3.128%	$85.5137	$85.51	$85.50	$85.50
7 purchase totals =	$900.25		$976.3236	$976.32	$976.35	$976.20