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	$6.27	11.442%	$6.9874	$6.99	$7.00	$7.00
Purchase #2	$142.88	4.113%	$148.7567	$148.76	$148.75	$148.80
Purchase #3	$30.40	11.647%	$33.9407	$33.94	$33.95	$33.90
Purchase #4	$213.57	9.219%	$233.259	$233.26	$233.25	$233.30
Purchase #5	$172.66	4.684%	$180.7474	$180.75	$180.75	$180.70
Purchase #6	$112.88	9.342%	$123.4252	$123.43	$123.45	$123.40
Purchase #7	$55.49	12.273%	$62.3003	$62.30	$62.30	$62.30
7 purchase totals =	$734.15		$789.4167	$789.43	$789.45	$789.40