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	$78.80	8.395%	$85.4153	$85.42	$85.40	$85.40
Purchase #2	$71.52	7.463%	$76.8575	$76.86	$76.85	$76.90
Purchase #3	$165.82	5.286%	$174.5852	$174.59	$174.60	$174.60
Purchase #4	$62.46	6.206%	$66.3363	$66.34	$66.35	$66.30
Purchase #5	$84.29	12.844%	$95.1162	$95.12	$95.10	$95.10
Purchase #6	$84.95	5.540%	$89.6562	$89.66	$89.65	$89.70
Purchase #7	$215.69	4.475%	$225.3421	$225.34	$225.35	$225.30
7 purchase totals =	$763.53		$813.3088	$813.33	$813.30	$813.30