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	$120.40	5.735%	$127.3049	$127.30	$127.30	$127.30
Purchase #2	$78.99	12.832%	$89.126	$89.13	$89.15	$89.10
Purchase #3	$41.53	12.791%	$46.8421	$46.84	$46.85	$46.80
Purchase #4	$152.61	3.835%	$158.4626	$158.46	$158.45	$158.50
Purchase #5	$151.72	7.246%	$162.7136	$162.71	$162.70	$162.70
Purchase #6	$142.39	10.127%	$156.8098	$156.81	$156.80	$156.80
Purchase #7	$175.35	11.843%	$196.1167	$196.12	$196.10	$196.10
7 purchase totals =	$862.99		$937.3757	$937.37	$937.35	$937.30