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	$78.84	4.660%	$82.5139	$82.51	$82.50	$82.50
Purchase #2	$72.98	10.239%	$80.4524	$80.45	$80.45	$80.50
Purchase #3	$10.34	6.813%	$11.0445	$11.04	$11.05	$11.00
Purchase #4	$106.49	13.518%	$120.8853	$120.89	$120.90	$120.90
Purchase #5	$10.74	8.230%	$11.6239	$11.62	$11.60	$11.60
Purchase #6	$130.36	6.803%	$139.2284	$139.23	$139.25	$139.20
Purchase #7	$101.31	13.740%	$115.23	$115.23	$115.25	$115.20
7 purchase totals =	$511.06		$560.9784	$560.97	$561.00	$560.90