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	$45.94	10.526%	$50.7756	$50.78	$50.80	$50.80
Purchase #2	$220.59	4.165%	$229.7776	$229.78	$229.80	$229.80
Purchase #3	$243.42	6.717%	$259.7705	$259.77	$259.75	$259.80
Purchase #4	$221.40	5.360%	$233.267	$233.27	$233.25	$233.30
Purchase #5	$89.60	5.340%	$94.3846	$94.38	$94.40	$94.40
Purchase #6	$92.25	9.434%	$100.9529	$100.95	$100.95	$101.00
Purchase #7	$211.51	5.160%	$222.4239	$222.42	$222.40	$222.40
7 purchase totals =	$1,124.71		$1,191.3521	$1,191.35	$1,191.35	$1,191.50