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	$91.68	4.821%	$96.0999	$96.10	$96.10	$96.10
Purchase #2	$59.89	4.614%	$62.6533	$62.65	$62.65	$62.70
Purchase #3	$90.63	9.236%	$99.0006	$99.00	$99.00	$99.00
Purchase #4	$70.71	11.522%	$78.8572	$78.86	$78.85	$78.90
Purchase #5	$248.43	9.658%	$272.4234	$272.42	$272.40	$272.40
Purchase #6	$234.33	3.602%	$242.7706	$242.77	$242.75	$242.80
Purchase #7	$69.88	8.437%	$75.7758	$75.78	$75.80	$75.80
7 purchase totals =	$865.55		$927.5808	$927.58	$927.55	$927.70