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	$20.57	13.234%	$23.2922	$23.29	$23.30	$23.30
Purchase #2	$48.30	7.541%	$51.9423	$51.94	$51.95	$51.90
Purchase #3	$176.91	13.514%	$200.8176	$200.82	$200.80	$200.80
Purchase #4	$156.95	7.396%	$168.558	$168.56	$168.55	$168.60
Purchase #5	$95.33	10.245%	$105.0966	$105.10	$105.10	$105.10
Purchase #6	$45.57	11.726%	$50.9135	$50.91	$50.90	$50.90
Purchase #7	$61.82	13.147%	$69.9475	$69.95	$69.95	$69.90
7 purchase totals =	$605.45		$670.5677	$670.57	$670.55	$670.50