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	$102.57	9.170%	$111.9757	$111.98	$112.00	$112.00
Purchase #2	$100.40	13.185%	$113.6377	$113.64	$113.65	$113.60
Purchase #3	$204.27	13.398%	$231.6381	$231.64	$231.65	$231.60
Purchase #4	$90.66	9.321%	$99.1104	$99.11	$99.10	$99.10
Purchase #5	$226.33	3.804%	$234.9396	$234.94	$234.95	$234.90
Purchase #6	$128.52	11.681%	$143.5324	$143.53	$143.55	$143.50
Purchase #7	$29.63	12.401%	$33.3044	$33.30	$33.30	$33.30
7 purchase totals =	$882.38		$968.1383	$968.14	$968.20	$968.00