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	$154.91	10.364%	$170.9649	$170.96	$170.95	$171.00
Purchase #2	$249.47	7.631%	$268.5071	$268.51	$268.50	$268.50
Purchase #3	$182.58	9.700%	$200.2903	$200.29	$200.30	$200.30
Purchase #4	$93.82	12.841%	$105.8674	$105.87	$105.85	$105.90
Purchase #5	$56.93	9.454%	$62.3122	$62.31	$62.30	$62.30
Purchase #6	$207.36	12.615%	$233.5185	$233.52	$233.50	$233.50
Purchase #7	$158.78	12.353%	$178.3941	$178.39	$178.40	$178.40
7 purchase totals =	$1,103.85		$1,219.8545	$1,219.85	$1,219.80	$1,219.90