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	$206.66	6.256%	$219.5886	$219.59	$219.60	$219.60
Purchase #2	$211.79	10.438%	$233.8966	$233.90	$233.90	$233.90
Purchase #3	$157.55	11.341%	$175.4177	$175.42	$175.40	$175.40
Purchase #4	$147.57	10.154%	$162.5543	$162.55	$162.55	$162.60
Purchase #5	$207.65	12.316%	$233.2242	$233.22	$233.20	$233.20
Purchase #6	$74.86	10.576%	$82.7772	$82.78	$82.80	$82.80
Purchase #7	$131.66	8.687%	$143.0973	$143.10	$143.10	$143.10
7 purchase totals =	$1,137.74		$1,250.5559	$1,250.56	$1,250.55	$1,250.60