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	$113.44	12.132%	$127.2025	$127.20	$127.20	$127.20
Purchase #2	$139.31	6.788%	$148.7664	$148.77	$148.75	$148.80
Purchase #3	$111.98	4.415%	$116.9239	$116.92	$116.90	$116.90
Purchase #4	$41.78	6.781%	$44.6131	$44.61	$44.60	$44.60
Purchase #5	$19.65	8.546%	$21.3293	$21.33	$21.35	$21.30
Purchase #6	$250.85	7.442%	$269.5183	$269.52	$269.50	$269.50
Purchase #7	$55.53	10.794%	$61.5239	$61.52	$61.50	$61.50
7 purchase totals =	$732.54		$789.8774	$789.87	$789.80	$789.80