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	$240.43	12.601%	$270.7266	$270.73	$270.75	$270.70
Purchase #2	$103.31	7.827%	$111.3961	$111.40	$111.40	$111.40
Purchase #3	$13.66	13.251%	$15.4701	$15.47	$15.45	$15.50
Purchase #4	$132.97	5.576%	$140.3844	$140.38	$140.40	$140.40
Purchase #5	$37.77	13.793%	$42.9796	$42.98	$43.00	$43.00
Purchase #6	$20.66	6.790%	$22.0628	$22.06	$22.05	$22.10
Purchase #7	$143.58	13.464%	$162.9116	$162.91	$162.90	$162.90
7 purchase totals =	$692.38		$765.9312	$765.93	$765.95	$766.00