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	$175.58	6.804%	$187.5265	$187.53	$187.55	$187.50
Purchase #2	$86.55	4.323%	$90.2916	$90.29	$90.30	$90.30
Purchase #3	$91.50	13.600%	$103.944	$103.94	$103.95	$103.90
Purchase #4	$105.71	11.806%	$118.1901	$118.19	$118.20	$118.20
Purchase #5	$29.90	8.470%	$32.4325	$32.43	$32.45	$32.40
Purchase #6	$171.63	12.555%	$193.1781	$193.18	$193.20	$193.20
Purchase #7	$134.32	10.441%	$148.3444	$148.34	$148.35	$148.30
7 purchase totals =	$795.19		$873.9072	$873.90	$874.00	$873.80