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	$36.46	10.520%	$40.2956	$40.30	$40.30	$40.30
Purchase #2	$101.35	13.785%	$115.3211	$115.32	$115.30	$115.30
Purchase #3	$121.39	7.501%	$130.4955	$130.50	$130.50	$130.50
Purchase #4	$111.31	3.439%	$115.138	$115.14	$115.15	$115.10
Purchase #5	$142.63	7.593%	$153.4599	$153.46	$153.45	$153.50
Purchase #6	$6.41	3.407%	$6.6284	$6.63	$6.65	$6.60
Purchase #7	$53.63	10.514%	$59.2687	$59.27	$59.25	$59.30
7 purchase totals =	$573.18		$620.6072	$620.62	$620.60	$620.60