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	$177.98	4.598%	$186.1635	$186.16	$186.15	$186.20
Purchase #2	$99.30	4.186%	$103.4567	$103.46	$103.45	$103.50
Purchase #3	$78.91	7.841%	$85.0973	$85.10	$85.10	$85.10
Purchase #4	$77.80	10.860%	$86.2491	$86.25	$86.25	$86.20
Purchase #5	$36.87	3.814%	$38.2762	$38.28	$38.30	$38.30
Purchase #6	$27.80	13.757%	$31.6244	$31.62	$31.60	$31.60
Purchase #7	$88.48	8.831%	$96.2937	$96.29	$96.30	$96.30
7 purchase totals =	$587.14		$627.1609	$627.16	$627.15	$627.20