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	$26.35	9.478%	$28.8475	$28.85	$28.85	$28.80
Purchase #2	$234.73	6.454%	$249.8795	$249.88	$249.90	$249.90
Purchase #3	$16.68	13.773%	$18.9773	$18.98	$19.00	$19.00
Purchase #4	$216.60	3.352%	$223.8604	$223.86	$223.85	$223.90
Purchase #5	$250.89	13.537%	$284.853	$284.85	$284.85	$284.90
Purchase #6	$89.59	3.842%	$93.032	$93.03	$93.05	$93.00
Purchase #7	$50.41	3.455%	$52.1517	$52.15	$52.15	$52.20
7 purchase totals =	$885.25		$951.6014	$951.60	$951.65	$951.70