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	$48.30	8.687%	$52.4958	$52.50	$52.50	$52.50
Purchase #2	$162.96	6.435%	$173.4465	$173.45	$173.45	$173.40
Purchase #3	$91.65	9.709%	$100.5483	$100.55	$100.55	$100.50
Purchase #4	$39.90	6.400%	$42.4536	$42.45	$42.45	$42.50
Purchase #5	$85.99	12.352%	$96.6115	$96.61	$96.60	$96.60
Purchase #6	$133.48	10.189%	$147.0803	$147.08	$147.10	$147.10
Purchase #7	$74.32	6.505%	$79.1545	$79.15	$79.15	$79.20
7 purchase totals =	$636.60		$691.7905	$691.79	$691.80	$691.80