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	$139.82	12.688%	$157.5604	$157.56	$157.55	$157.60
Purchase #2	$220.72	8.578%	$239.6534	$239.65	$239.65	$239.70
Purchase #3	$172.53	10.686%	$190.9666	$190.97	$190.95	$191.00
Purchase #4	$28.59	9.106%	$31.1934	$31.19	$31.20	$31.20
Purchase #5	$81.33	13.360%	$92.1957	$92.20	$92.20	$92.20
Purchase #6	$250.60	5.579%	$264.581	$264.58	$264.60	$264.60
Purchase #7	$80.93	5.369%	$85.2751	$85.28	$85.30	$85.30
7 purchase totals =	$974.52		$1,061.4256	$1,061.43	$1,061.45	$1,061.60