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	$68.91	11.793%	$77.0366	$77.04	$77.05	$77.00
Purchase #2	$92.80	12.543%	$104.4399	$104.44	$104.45	$104.40
Purchase #3	$239.63	12.268%	$269.0278	$269.03	$269.05	$269.00
Purchase #4	$225.87	9.572%	$247.4903	$247.49	$247.50	$247.50
Purchase #5	$185.40	10.240%	$204.385	$204.39	$204.40	$204.40
Purchase #6	$77.76	5.853%	$82.3113	$82.31	$82.30	$82.30
Purchase #7	$29.54	5.850%	$31.2681	$31.27	$31.25	$31.30
7 purchase totals =	$919.91		$1,015.9590	$1,015.97	$1,016.00	$1,015.90