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	$205.94	6.783%	$219.9089	$219.91	$219.90	$219.90
Purchase #2	$37.70	11.763%	$42.1347	$42.13	$42.15	$42.10
Purchase #3	$26.70	7.775%	$28.7759	$28.78	$28.80	$28.80
Purchase #4	$34.56	5.733%	$36.5413	$36.54	$36.55	$36.50
Purchase #5	$34.26	12.159%	$38.4257	$38.43	$38.45	$38.40
Purchase #6	$41.73	13.827%	$47.5	$47.50	$47.50	$47.50
Purchase #7	$40.35	13.566%	$45.8239	$45.82	$45.80	$45.80
7 purchase totals =	$421.24		$459.1104	$459.11	$459.15	$459.00