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	$68.52	10.584%	$75.7722	$75.77	$75.75	$75.80
Purchase #2	$76.59	3.645%	$79.3817	$79.38	$79.40	$79.40
Purchase #3	$67.29	8.203%	$72.8098	$72.81	$72.80	$72.80
Purchase #4	$82.78	8.677%	$89.9628	$89.96	$89.95	$90.00
Purchase #5	$139.83	5.628%	$147.6996	$147.70	$147.70	$147.70
Purchase #6	$231.34	3.858%	$240.2651	$240.27	$240.25	$240.30
Purchase #7	$141.59	6.139%	$150.2822	$150.28	$150.30	$150.30
7 purchase totals =	$807.94		$856.1734	$856.17	$856.15	$856.30