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	$25.70	10.144%	$28.307	$28.31	$28.30	$28.30
Purchase #2	$88.56	13.396%	$100.4235	$100.42	$100.40	$100.40
Purchase #3	$139.69	10.288%	$154.0613	$154.06	$154.05	$154.10
Purchase #4	$166.81	7.253%	$178.9087	$178.91	$178.90	$178.90
Purchase #5	$246.29	13.310%	$279.0712	$279.07	$279.05	$279.10
Purchase #6	$243.27	9.667%	$266.7869	$266.79	$266.80	$266.80
Purchase #7	$217.63	7.478%	$233.9044	$233.90	$233.90	$233.90
7 purchase totals =	$1,127.95		$1,241.4630	$1,241.46	$1,241.40	$1,241.50