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	$128.47	11.811%	$143.6436	$143.64	$143.65	$143.60
Purchase #2	$18.97	8.540%	$20.59	$20.59	$20.60	$20.60
Purchase #3	$38.97	9.535%	$42.6858	$42.69	$42.70	$42.70
Purchase #4	$231.82	8.195%	$250.8176	$250.82	$250.80	$250.80
Purchase #5	$16.73	9.465%	$18.3135	$18.31	$18.30	$18.30
Purchase #6	$237.47	5.451%	$250.4145	$250.41	$250.40	$250.40
Purchase #7	$39.34	5.469%	$41.4915	$41.49	$41.50	$41.50
7 purchase totals =	$711.77		$767.9565	$767.95	$767.95	$767.90