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	$150.66	5.358%	$158.7324	$158.73	$158.75	$158.70
Purchase #2	$225.38	4.632%	$235.8196	$235.82	$235.80	$235.80
Purchase #3	$89.59	3.431%	$92.6638	$92.66	$92.65	$92.70
Purchase #4	$101.76	7.139%	$109.0246	$109.02	$109.00	$109.00
Purchase #5	$24.96	11.718%	$27.8848	$27.88	$27.90	$27.90
Purchase #6	$94.99	11.195%	$105.6241	$105.62	$105.60	$105.60
Purchase #7	$67.93	3.687%	$70.4346	$70.43	$70.45	$70.40
7 purchase totals =	$755.27		$800.1839	$800.16	$800.15	$800.10