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	$123.69	3.402%	$127.8979	$127.90	$127.90	$127.90
Purchase #2	$243.58	6.175%	$258.6211	$258.62	$258.60	$258.60
Purchase #3	$55.84	12.327%	$62.7234	$62.72	$62.70	$62.70
Purchase #4	$249.38	5.765%	$263.7568	$263.76	$263.75	$263.80
Purchase #5	$241.52	11.380%	$269.005	$269.01	$269.00	$269.00
Purchase #6	$170.96	9.723%	$187.5824	$187.58	$187.60	$187.60
Purchase #7	$170.63	5.167%	$179.4465	$179.45	$179.45	$179.40
7 purchase totals =	$1,255.60		$1,349.0331	$1,349.04	$1,349.00	$1,349.00