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	$238.75	10.616%	$264.0957	$264.10	$264.10	$264.10
Purchase #2	$206.67	3.418%	$213.734	$213.73	$213.75	$213.70
Purchase #3	$230.54	8.683%	$250.5578	$250.56	$250.55	$250.60
Purchase #4	$90.54	11.446%	$100.9032	$100.90	$100.90	$100.90
Purchase #5	$130.52	11.762%	$145.8718	$145.87	$145.85	$145.90
Purchase #6	$160.48	8.294%	$173.7902	$173.79	$173.80	$173.80
Purchase #7	$66.34	12.665%	$74.742	$74.74	$74.75	$74.70
7 purchase totals =	$1,123.84		$1,223.6947	$1,223.69	$1,223.70	$1,223.70