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	$29.58	11.191%	$32.8903	$32.89	$32.90	$32.90
Purchase #2	$131.57	12.354%	$147.8242	$147.82	$147.80	$147.80
Purchase #3	$153.52	13.813%	$174.7257	$174.73	$174.75	$174.70
Purchase #4	$200.97	11.684%	$224.4513	$224.45	$224.45	$224.50
Purchase #5	$217.56	7.289%	$233.4179	$233.42	$233.40	$233.40
Purchase #6	$136.30	5.218%	$143.4121	$143.41	$143.40	$143.40
Purchase #7	$57.34	12.726%	$64.6371	$64.64	$64.65	$64.60
7 purchase totals =	$926.84		$1,021.3586	$1,021.36	$1,021.35	$1,021.30