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	$20.38	9.546%	$22.3255	$22.33	$22.35	$22.30
Purchase #2	$220.71	13.348%	$250.1704	$250.17	$250.15	$250.20
Purchase #3	$38.74	9.270%	$42.3312	$42.33	$42.35	$42.30
Purchase #4	$113.77	8.245%	$123.1503	$123.15	$123.15	$123.20
Purchase #5	$185.29	11.558%	$206.7058	$206.71	$206.70	$206.70
Purchase #6	$65.83	8.193%	$71.2235	$71.22	$71.20	$71.20
Purchase #7	$162.47	4.450%	$169.6999	$169.70	$169.70	$169.70
7 purchase totals =	$807.19		$885.6066	$885.61	$885.60	$885.60