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	$133.77	13.280%	$151.5347	$151.53	$151.55	$151.50
Purchase #2	$63.32	9.573%	$69.3816	$69.38	$69.40	$69.40
Purchase #3	$199.39	5.629%	$210.6137	$210.61	$210.60	$210.60
Purchase #4	$189.69	5.358%	$199.8536	$199.85	$199.85	$199.90
Purchase #5	$67.85	7.246%	$72.7664	$72.77	$72.75	$72.80
Purchase #6	$121.99	8.183%	$131.9724	$131.97	$131.95	$132.00
Purchase #7	$151.49	9.263%	$165.5225	$165.52	$165.50	$165.50
7 purchase totals =	$927.50		$1,001.6449	$1,001.63	$1,001.60	$1,001.70