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	$160.58	6.666%	$171.2843	$171.28	$171.30	$171.30
Purchase #2	$65.90	7.471%	$70.8234	$70.82	$70.80	$70.80
Purchase #3	$79.98	13.158%	$90.5038	$90.50	$90.50	$90.50
Purchase #4	$26.90	10.299%	$29.6704	$29.67	$29.65	$29.70
Purchase #5	$141.72	7.785%	$152.7529	$152.75	$152.75	$152.80
Purchase #6	$224.76	9.321%	$245.7099	$245.71	$245.70	$245.70
Purchase #7	$87.28	9.450%	$95.528	$95.53	$95.55	$95.50
7 purchase totals =	$787.12		$856.2727	$856.26	$856.25	$856.30