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	$148.71	6.188%	$157.9122	$157.91	$157.90	$157.90
Purchase #2	$95.42	7.637%	$102.7072	$102.71	$102.70	$102.70
Purchase #3	$54.82	8.253%	$59.3443	$59.34	$59.35	$59.30
Purchase #4	$212.35	7.660%	$228.616	$228.62	$228.60	$228.60
Purchase #5	$61.38	11.387%	$68.3693	$68.37	$68.35	$68.40
Purchase #6	$92.80	11.349%	$103.3319	$103.33	$103.35	$103.30
Purchase #7	$75.80	13.300%	$85.8814	$85.88	$85.90	$85.90
7 purchase totals =	$741.28		$806.1623	$806.16	$806.15	$806.10