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	$112.53	6.452%	$119.7904	$119.79	$119.80	$119.80
Purchase #2	$242.40	11.746%	$270.8723	$270.87	$270.85	$270.90
Purchase #3	$151.40	13.692%	$172.1297	$172.13	$172.15	$172.10
Purchase #4	$64.91	11.499%	$72.374	$72.37	$72.35	$72.40
Purchase #5	$74.63	6.821%	$79.7205	$79.72	$79.70	$79.70
Purchase #6	$112.45	10.572%	$124.3382	$124.34	$124.35	$124.30
Purchase #7	$133.38	4.771%	$139.7436	$139.74	$139.75	$139.70
7 purchase totals =	$891.70		$978.9687	$978.96	$978.95	$978.90