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	$236.71	7.773%	$255.1095	$255.11	$255.10	$255.10
Purchase #2	$250.82	3.268%	$259.0168	$259.02	$259.00	$259.00
Purchase #3	$211.39	9.470%	$231.4086	$231.41	$231.40	$231.40
Purchase #4	$178.48	3.832%	$185.3194	$185.32	$185.30	$185.30
Purchase #5	$165.69	6.605%	$176.6338	$176.63	$176.65	$176.60
Purchase #6	$30.73	5.230%	$32.3372	$32.34	$32.35	$32.30
Purchase #7	$234.69	13.802%	$267.0819	$267.08	$267.10	$267.10
7 purchase totals =	$1,308.51		$1,406.9072	$1,406.91	$1,406.90	$1,406.80