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	$71.37	12.118%	$80.0186	$80.02	$80.00	$80.00
Purchase #2	$124.70	7.657%	$134.2483	$134.25	$134.25	$134.20
Purchase #3	$137.43	10.269%	$151.5427	$151.54	$151.55	$151.50
Purchase #4	$82.39	12.116%	$92.3724	$92.37	$92.35	$92.40
Purchase #5	$51.53	8.316%	$55.8152	$55.82	$55.80	$55.80
Purchase #6	$129.43	12.262%	$145.3007	$145.30	$145.30	$145.30
Purchase #7	$12.68	12.314%	$14.2414	$14.24	$14.25	$14.20
7 purchase totals =	$609.53		$673.5393	$673.54	$673.50	$673.40