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	$209.50	11.423%	$233.4312	$233.43	$233.45	$233.40
Purchase #2	$85.30	11.873%	$95.4277	$95.43	$95.45	$95.40
Purchase #3	$206.93	6.815%	$221.0323	$221.03	$221.05	$221.00
Purchase #4	$72.95	13.397%	$82.7231	$82.72	$82.70	$82.70
Purchase #5	$191.63	10.337%	$211.4388	$211.44	$211.45	$211.40
Purchase #6	$78.49	4.367%	$81.9177	$81.92	$81.90	$81.90
Purchase #7	$61.60	8.143%	$66.6161	$66.62	$66.60	$66.60
7 purchase totals =	$906.40		$992.5869	$992.59	$992.60	$992.40