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	$225.87	10.502%	$249.5909	$249.59	$249.60	$249.60
Purchase #2	$83.79	9.430%	$91.6914	$91.69	$91.70	$91.70
Purchase #3	$122.83	7.510%	$132.0545	$132.05	$132.05	$132.10
Purchase #4	$65.44	3.356%	$67.6362	$67.64	$67.65	$67.60
Purchase #5	$88.25	3.705%	$91.5197	$91.52	$91.50	$91.50
Purchase #6	$38.27	6.734%	$40.8471	$40.85	$40.85	$40.80
Purchase #7	$110.49	6.822%	$118.0276	$118.03	$118.05	$118.00
7 purchase totals =	$734.94		$791.3674	$791.37	$791.40	$791.30