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	$141.32	8.305%	$153.0566	$153.06	$153.05	$153.10
Purchase #2	$243.87	11.363%	$271.5809	$271.58	$271.60	$271.60
Purchase #3	$133.82	5.465%	$141.1333	$141.13	$141.15	$141.10
Purchase #4	$219.46	4.802%	$229.9985	$230.00	$230.00	$230.00
Purchase #5	$93.76	12.354%	$105.3431	$105.34	$105.35	$105.30
Purchase #6	$35.31	13.393%	$40.0391	$40.04	$40.05	$40.00
Purchase #7	$81.46	9.777%	$89.4243	$89.42	$89.40	$89.40
7 purchase totals =	$949.00		$1,030.5758	$1,030.57	$1,030.60	$1,030.50