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	$99.62	6.326%	$105.922	$105.92	$105.90	$105.90
Purchase #2	$234.74	11.458%	$261.6365	$261.64	$261.65	$261.60
Purchase #3	$18.53	13.114%	$20.96	$20.96	$20.95	$21.00
Purchase #4	$248.97	5.779%	$263.358	$263.36	$263.35	$263.40
Purchase #5	$95.91	13.809%	$109.1542	$109.15	$109.15	$109.20
Purchase #6	$127.80	10.845%	$141.6599	$141.66	$141.65	$141.70
Purchase #7	$59.77	9.179%	$65.2563	$65.26	$65.25	$65.30
7 purchase totals =	$885.34		$967.9469	$967.95	$967.90	$968.10