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	$152.79	9.872%	$167.8734	$167.87	$167.85	$167.90
Purchase #2	$39.75	8.717%	$43.215	$43.22	$43.20	$43.20
Purchase #3	$39.43	6.757%	$42.0943	$42.09	$42.10	$42.10
Purchase #4	$80.92	6.375%	$86.0787	$86.08	$86.10	$86.10
Purchase #5	$113.98	12.867%	$128.6458	$128.65	$128.65	$128.60
Purchase #6	$29.39	7.179%	$31.4999	$31.50	$31.50	$31.50
Purchase #7	$73.76	5.152%	$77.5601	$77.56	$77.55	$77.60
7 purchase totals =	$530.02		$576.9672	$576.97	$576.95	$577.00