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	$249.86	7.165%	$267.7625	$267.76	$267.75	$267.80
Purchase #2	$107.71	3.404%	$111.3764	$111.38	$111.40	$111.40
Purchase #3	$22.75	10.472%	$25.1324	$25.13	$25.15	$25.10
Purchase #4	$121.51	8.789%	$132.1895	$132.19	$132.20	$132.20
Purchase #5	$91.86	9.561%	$100.6427	$100.64	$100.65	$100.60
Purchase #6	$165.90	7.561%	$178.4437	$178.44	$178.45	$178.40
Purchase #7	$114.96	10.719%	$127.2826	$127.28	$127.30	$127.30
7 purchase totals =	$874.55		$942.8298	$942.82	$942.90	$942.80