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	$250.69	11.844%	$280.3817	$280.38	$280.40	$280.40
Purchase #2	$154.36	11.820%	$172.6054	$172.61	$172.60	$172.60
Purchase #3	$181.35	10.761%	$200.8651	$200.87	$200.85	$200.90
Purchase #4	$29.66	3.535%	$30.7085	$30.71	$30.70	$30.70
Purchase #5	$145.85	3.650%	$151.1735	$151.17	$151.15	$151.20
Purchase #6	$27.77	6.271%	$29.5115	$29.51	$29.50	$29.50
Purchase #7	$207.63	3.748%	$215.412	$215.41	$215.40	$215.40
7 purchase totals =	$997.31		$1,080.6577	$1,080.66	$1,080.60	$1,080.70