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	$165.41	8.764%	$179.9065	$179.91	$179.90	$179.90
Purchase #2	$202.46	10.457%	$223.6312	$223.63	$223.65	$223.60
Purchase #3	$55.25	4.454%	$57.7108	$57.71	$57.70	$57.70
Purchase #4	$203.75	8.244%	$220.5472	$220.55	$220.55	$220.50
Purchase #5	$52.95	3.518%	$54.8128	$54.81	$54.80	$54.80
Purchase #6	$123.35	11.568%	$137.6191	$137.62	$137.60	$137.60
Purchase #7	$109.39	13.173%	$123.7999	$123.80	$123.80	$123.80
7 purchase totals =	$912.56		$998.0275	$998.03	$998.00	$997.90