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	$21.65	11.272%	$24.0904	$24.09	$24.10	$24.10
Purchase #2	$90.35	11.304%	$100.5632	$100.56	$100.55	$100.60
Purchase #3	$224.48	13.717%	$255.2719	$255.27	$255.25	$255.30
Purchase #4	$171.67	3.734%	$178.0802	$178.08	$178.10	$178.10
Purchase #5	$37.31	11.114%	$41.4566	$41.46	$41.45	$41.50
Purchase #6	$237.76	10.163%	$261.9235	$261.92	$261.90	$261.90
Purchase #7	$224.48	9.293%	$245.3409	$245.34	$245.35	$245.30
7 purchase totals =	$1,007.70		$1,106.7267	$1,106.72	$1,106.70	$1,106.80