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	$99.64	4.650%	$104.2733	$104.27	$104.25	$104.30
Purchase #2	$89.41	11.135%	$99.3658	$99.37	$99.35	$99.40
Purchase #3	$28.98	7.129%	$31.046	$31.05	$31.05	$31.00
Purchase #4	$103.69	7.148%	$111.1018	$111.10	$111.10	$111.10
Purchase #5	$246.63	10.148%	$271.658	$271.66	$271.65	$271.70
Purchase #6	$144.83	10.377%	$159.859	$159.86	$159.85	$159.90
Purchase #7	$110.60	10.431%	$122.1367	$122.14	$122.15	$122.10
7 purchase totals =	$823.78		$899.4406	$899.45	$899.40	$899.50