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	$200.34	6.266%	$212.8933	$212.89	$212.90	$212.90
Purchase #2	$131.82	9.195%	$143.9408	$143.94	$143.95	$143.90
Purchase #3	$130.88	11.110%	$145.4208	$145.42	$145.40	$145.40
Purchase #4	$11.78	5.108%	$12.3817	$12.38	$12.40	$12.40
Purchase #5	$137.98	7.658%	$148.5465	$148.55	$148.55	$148.50
Purchase #6	$214.52	13.483%	$243.4437	$243.44	$243.45	$243.40
Purchase #7	$236.95	13.154%	$268.1184	$268.12	$268.10	$268.10
7 purchase totals =	$1,064.27		$1,174.7452	$1,174.74	$1,174.75	$1,174.60