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	$82.89	9.506%	$90.7695	$90.77	$90.75	$90.80
Purchase #2	$16.32	4.624%	$17.0746	$17.07	$17.05	$17.10
Purchase #3	$233.64	8.507%	$253.5158	$253.52	$253.50	$253.50
Purchase #4	$74.95	6.789%	$80.0384	$80.04	$80.05	$80.00
Purchase #5	$34.41	5.799%	$36.4054	$36.41	$36.40	$36.40
Purchase #6	$72.91	12.414%	$81.961	$81.96	$81.95	$82.00
Purchase #7	$109.49	4.225%	$114.116	$114.12	$114.10	$114.10
7 purchase totals =	$624.61		$673.8807	$673.89	$673.80	$673.90