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	7.153%	$84.4794	$84.48	$84.50	$84.50
Purchase #2	$120.98	5.680%	$127.8517	$127.85	$127.85	$127.90
Purchase #3	$247.61	9.821%	$271.9278	$271.93	$271.95	$271.90
Purchase #4	$131.82	5.414%	$138.9567	$138.96	$138.95	$139.00
Purchase #5	$55.63	3.108%	$57.359	$57.36	$57.35	$57.40
Purchase #6	$86.95	3.679%	$90.1489	$90.15	$90.15	$90.10
Purchase #7	$51.30	8.786%	$55.8072	$55.81	$55.80	$55.80
7 purchase totals =	$773.13		$826.5307	$826.54	$826.55	$826.60