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	$76.40	11.516%	$85.1982	$85.20	$85.20	$85.20
Purchase #2	$96.58	9.700%	$105.9483	$105.95	$105.95	$105.90
Purchase #3	$179.80	10.761%	$199.1483	$199.15	$199.15	$199.10
Purchase #4	$47.31	7.642%	$50.9254	$50.93	$50.95	$50.90
Purchase #5	$104.69	6.546%	$111.543	$111.54	$111.55	$111.50
Purchase #6	$140.81	12.684%	$158.6703	$158.67	$158.65	$158.70
Purchase #7	$87.73	4.432%	$91.6182	$91.62	$91.60	$91.60
7 purchase totals =	$733.32		$803.0517	$803.06	$803.05	$802.90