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	$172.49	8.310%	$186.8239	$186.82	$186.80	$186.80
Purchase #2	$216.27	4.705%	$226.4455	$226.45	$226.45	$226.40
Purchase #3	$65.75	11.654%	$73.4125	$73.41	$73.40	$73.40
Purchase #4	$35.32	6.381%	$37.5738	$37.57	$37.55	$37.60
Purchase #5	$42.86	5.258%	$45.1136	$45.11	$45.10	$45.10
Purchase #6	$142.36	8.425%	$154.3538	$154.35	$154.35	$154.40
Purchase #7	$83.85	3.629%	$86.8929	$86.89	$86.90	$86.90
7 purchase totals =	$758.90		$810.6160	$810.60	$810.55	$810.60