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	$115.92	6.237%	$123.1499	$123.15	$123.15	$123.10
Purchase #2	$56.27	10.441%	$62.1452	$62.15	$62.15	$62.10
Purchase #3	$250.73	7.716%	$270.0763	$270.08	$270.10	$270.10
Purchase #4	$64.75	3.501%	$67.0169	$67.02	$67.00	$67.00
Purchase #5	$99.66	5.524%	$105.1652	$105.17	$105.15	$105.20
Purchase #6	$128.63	11.131%	$142.9478	$142.95	$142.95	$142.90
Purchase #7	$68.28	10.810%	$75.6611	$75.66	$75.65	$75.70
7 purchase totals =	$784.24		$846.1624	$846.18	$846.15	$846.10