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	$51.28	11.107%	$56.9757	$56.98	$57.00	$57.00
Purchase #2	$236.87	9.294%	$258.8847	$258.88	$258.90	$258.90
Purchase #3	$85.33	10.492%	$94.2828	$94.28	$94.30	$94.30
Purchase #4	$11.57	12.812%	$13.0523	$13.05	$13.05	$13.10
Purchase #5	$167.83	7.760%	$180.8536	$180.85	$180.85	$180.90
Purchase #6	$185.75	10.418%	$205.1014	$205.10	$205.10	$205.10
Purchase #7	$212.91	4.544%	$222.5846	$222.58	$222.60	$222.60
7 purchase totals =	$951.54		$1,031.7351	$1,031.72	$1,031.80	$1,031.90