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	$36.74	7.464%	$39.4823	$39.48	$39.50	$39.50
Purchase #2	$112.97	13.568%	$128.2978	$128.30	$128.30	$128.30
Purchase #3	$203.59	6.435%	$216.691	$216.69	$216.70	$216.70
Purchase #4	$14.55	4.345%	$15.1822	$15.18	$15.20	$15.20
Purchase #5	$183.39	3.689%	$190.1553	$190.16	$190.15	$190.20
Purchase #6	$98.78	7.291%	$105.982	$105.98	$106.00	$106.00
Purchase #7	$89.89	11.640%	$100.3532	$100.35	$100.35	$100.40
7 purchase totals =	$739.91		$796.1438	$796.14	$796.20	$796.30