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	$70.37	12.191%	$78.9488	$78.95	$78.95	$78.90
Purchase #2	$97.73	3.443%	$101.0948	$101.09	$101.10	$101.10
Purchase #3	$155.58	6.546%	$165.7643	$165.76	$165.75	$165.80
Purchase #4	$193.57	11.339%	$215.5189	$215.52	$215.50	$215.50
Purchase #5	$85.54	4.143%	$89.0839	$89.08	$89.10	$89.10
Purchase #6	$139.57	4.433%	$145.7571	$145.76	$145.75	$145.80
Purchase #7	$54.88	6.345%	$58.3621	$58.36	$58.35	$58.40
7 purchase totals =	$797.24		$854.5299	$854.52	$854.50	$854.60