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	$46.89	7.803%	$50.5488	$50.55	$50.55	$50.50
Purchase #2	$103.40	11.517%	$115.3086	$115.31	$115.30	$115.30
Purchase #3	$172.37	8.152%	$186.4216	$186.42	$186.40	$186.40
Purchase #4	$175.40	6.406%	$186.6361	$186.64	$186.65	$186.60
Purchase #5	$59.63	4.415%	$62.2627	$62.26	$62.25	$62.30
Purchase #6	$156.86	3.443%	$162.2607	$162.26	$162.25	$162.30
Purchase #7	$244.30	11.104%	$271.4271	$271.43	$271.45	$271.40
7 purchase totals =	$958.85		$1,034.8656	$1,034.87	$1,034.85	$1,034.80