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	$122.95	13.823%	$139.9454	$139.95	$139.95	$139.90
Purchase #2	$229.48	10.770%	$254.195	$254.20	$254.20	$254.20
Purchase #3	$140.54	13.535%	$159.5621	$159.56	$159.55	$159.60
Purchase #4	$155.62	8.327%	$168.5785	$168.58	$168.60	$168.60
Purchase #5	$71.93	9.486%	$78.7533	$78.75	$78.75	$78.80
Purchase #6	$109.49	5.329%	$115.3247	$115.32	$115.30	$115.30
Purchase #7	$150.53	11.665%	$168.0893	$168.09	$168.10	$168.10
7 purchase totals =	$980.54		$1,084.4483	$1,084.45	$1,084.45	$1,084.50