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	$128.93	3.439%	$133.3639	$133.36	$133.35	$133.40
Purchase #2	$161.94	5.790%	$171.3163	$171.32	$171.30	$171.30
Purchase #3	$136.43	10.164%	$150.2967	$150.30	$150.30	$150.30
Purchase #4	$49.60	10.549%	$54.8323	$54.83	$54.85	$54.80
Purchase #5	$231.53	4.650%	$242.2961	$242.30	$242.30	$242.30
Purchase #6	$155.95	9.759%	$171.1692	$171.17	$171.15	$171.20
Purchase #7	$74.75	6.422%	$79.5504	$79.55	$79.55	$79.60
7 purchase totals =	$939.13		$1,002.8249	$1,002.83	$1,002.80	$1,002.90