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	$95.70	7.676%	$103.0459	$103.05	$103.05	$103.00
Purchase #2	$115.98	6.444%	$123.4538	$123.45	$123.45	$123.50
Purchase #3	$180.91	10.353%	$199.6396	$199.64	$199.65	$199.60
Purchase #4	$138.35	8.831%	$150.5677	$150.57	$150.55	$150.60
Purchase #5	$95.78	13.830%	$109.0264	$109.03	$109.05	$109.00
Purchase #6	$45.47	3.593%	$47.1037	$47.10	$47.10	$47.10
Purchase #7	$224.32	6.250%	$238.34	$238.34	$238.35	$238.30
7 purchase totals =	$896.51		$971.1771	$971.18	$971.20	$971.10