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	$31.80	6.399%	$33.8349	$33.83	$33.85	$33.80
Purchase #2	$64.31	10.336%	$70.9571	$70.96	$70.95	$71.00
Purchase #3	$176.69	6.125%	$187.5123	$187.51	$187.50	$187.50
Purchase #4	$126.27	12.550%	$142.1169	$142.12	$142.10	$142.10
Purchase #5	$102.55	6.318%	$109.0291	$109.03	$109.05	$109.00
Purchase #6	$120.49	6.252%	$128.023	$128.02	$128.00	$128.00
Purchase #7	$124.39	4.473%	$129.954	$129.95	$129.95	$130.00
7 purchase totals =	$746.50		$801.4273	$801.42	$801.40	$801.40