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	$124.90	12.167%	$140.0966	$140.10	$140.10	$140.10
Purchase #2	$179.98	13.849%	$204.9054	$204.91	$204.90	$204.90
Purchase #3	$177.95	11.476%	$198.3715	$198.37	$198.35	$198.40
Purchase #4	$51.29	7.793%	$55.287	$55.29	$55.30	$55.30
Purchase #5	$54.87	9.275%	$59.9592	$59.96	$59.95	$60.00
Purchase #6	$83.54	7.343%	$89.6743	$89.67	$89.65	$89.70
Purchase #7	$5.73	12.816%	$6.4644	$6.46	$6.45	$6.50
7 purchase totals =	$678.26		$754.7584	$754.76	$754.70	$754.90