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	$211.85	13.727%	$240.9306	$240.93	$240.95	$240.90
Purchase #2	$115.78	7.646%	$124.6325	$124.63	$124.65	$124.60
Purchase #3	$123.82	4.168%	$128.9808	$128.98	$129.00	$129.00
Purchase #4	$114.72	13.645%	$130.3735	$130.37	$130.35	$130.40
Purchase #5	$131.29	6.575%	$139.9223	$139.92	$139.90	$139.90
Purchase #6	$145.26	13.427%	$164.7641	$164.76	$164.75	$164.80
Purchase #7	$44.73	8.353%	$48.4663	$48.47	$48.45	$48.50
7 purchase totals =	$887.45		$978.0701	$978.06	$978.05	$978.10