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	$148.90	3.622%	$154.2932	$154.29	$154.30	$154.30
Purchase #2	$50.39	8.483%	$54.6646	$54.66	$54.65	$54.70
Purchase #3	$78.85	13.599%	$89.5728	$89.57	$89.55	$89.60
Purchase #4	$149.34	11.435%	$166.417	$166.42	$166.40	$166.40
Purchase #5	$212.56	4.418%	$221.9509	$221.95	$221.95	$222.00
Purchase #6	$99.70	8.842%	$108.5155	$108.52	$108.50	$108.50
Purchase #7	$183.68	4.787%	$192.4728	$192.47	$192.45	$192.50
7 purchase totals =	$923.42		$987.8868	$987.88	$987.80	$988.00