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	$6.28	5.154%	$6.6037	$6.60	$6.60	$6.60
Purchase #2	$101.98	4.617%	$106.6884	$106.69	$106.70	$106.70
Purchase #3	$131.41	6.536%	$139.999	$140.00	$140.00	$140.00
Purchase #4	$28.77	12.390%	$32.3346	$32.33	$32.35	$32.30
Purchase #5	$32.29	6.427%	$34.3653	$34.37	$34.35	$34.40
Purchase #6	$81.64	12.473%	$91.823	$91.82	$91.80	$91.80
Purchase #7	$54.59	9.111%	$59.5637	$59.56	$59.55	$59.60
7 purchase totals =	$436.96		$471.3777	$471.37	$471.35	$471.40