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	$231.56	7.208%	$248.2508	$248.25	$248.25	$248.30
Purchase #2	$22.35	9.720%	$24.5224	$24.52	$24.50	$24.50
Purchase #3	$104.69	11.114%	$116.3252	$116.33	$116.35	$116.30
Purchase #4	$102.95	4.119%	$107.1905	$107.19	$107.20	$107.20
Purchase #5	$78.70	9.655%	$86.2985	$86.30	$86.30	$86.30
Purchase #6	$158.81	4.810%	$166.4488	$166.45	$166.45	$166.40
Purchase #7	$103.59	5.731%	$109.5267	$109.53	$109.55	$109.50
7 purchase totals =	$802.65		$858.5629	$858.57	$858.60	$858.50