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	$34.98	7.174%	$37.4895	$37.49	$37.50	$37.50
Purchase #2	$138.83	12.850%	$156.6697	$156.67	$156.65	$156.70
Purchase #3	$71.69	8.834%	$78.0231	$78.02	$78.00	$78.00
Purchase #4	$226.50	11.243%	$251.9654	$251.97	$251.95	$252.00
Purchase #5	$199.85	13.142%	$226.1143	$226.11	$226.10	$226.10
Purchase #6	$114.80	8.842%	$124.9506	$124.95	$124.95	$125.00
Purchase #7	$120.25	6.422%	$127.9725	$127.97	$127.95	$128.00
7 purchase totals =	$906.90		$1,003.1851	$1,003.18	$1,003.10	$1,003.30