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	$19.26	6.302%	$20.4738	$20.47	$20.45	$20.50
Purchase #2	$11.85	3.812%	$12.3017	$12.30	$12.30	$12.30
Purchase #3	$168.71	8.537%	$183.1128	$183.11	$183.10	$183.10
Purchase #4	$60.48	12.266%	$67.8985	$67.90	$67.90	$67.90
Purchase #5	$149.91	10.431%	$165.5471	$165.55	$165.55	$165.50
Purchase #6	$73.60	6.326%	$78.2559	$78.26	$78.25	$78.30
Purchase #7	$189.64	3.831%	$196.9051	$196.91	$196.90	$196.90
7 purchase totals =	$673.45		$724.4949	$724.50	$724.45	$724.50