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	$31.56	10.396%	$34.841	$34.84	$34.85	$34.80
Purchase #2	$51.50	5.759%	$54.4659	$54.47	$54.45	$54.50
Purchase #3	$170.36	5.497%	$179.7247	$179.72	$179.70	$179.70
Purchase #4	$146.52	4.169%	$152.6284	$152.63	$152.65	$152.60
Purchase #5	$151.71	5.396%	$159.8963	$159.90	$159.90	$159.90
Purchase #6	$203.46	10.765%	$225.3625	$225.36	$225.35	$225.40
Purchase #7	$218.78	13.639%	$248.6194	$248.62	$248.60	$248.60
7 purchase totals =	$973.89		$1,055.5382	$1,055.54	$1,055.50	$1,055.50