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	$37.45	9.157%	$40.8793	$40.88	$40.90	$40.90
Purchase #2	$152.43	4.210%	$158.8473	$158.85	$158.85	$158.80
Purchase #3	$107.86	7.865%	$116.3432	$116.34	$116.35	$116.30
Purchase #4	$185.76	11.453%	$207.0351	$207.04	$207.05	$207.00
Purchase #5	$248.66	6.447%	$264.6911	$264.69	$264.70	$264.70
Purchase #6	$53.72	3.460%	$55.5787	$55.58	$55.60	$55.60
Purchase #7	$181.94	4.105%	$189.4086	$189.41	$189.40	$189.40
7 purchase totals =	$967.82		$1,032.7833	$1,032.79	$1,032.85	$1,032.70