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	$20.38	7.404%	$21.8889	$21.89	$21.90	$21.90
Purchase #2	$132.95	10.599%	$147.0414	$147.04	$147.05	$147.00
Purchase #3	$159.43	5.785%	$168.653	$168.65	$168.65	$168.70
Purchase #4	$45.52	7.855%	$49.0956	$49.10	$49.10	$49.10
Purchase #5	$179.69	6.164%	$190.7661	$190.77	$190.75	$190.80
Purchase #6	$101.76	7.764%	$109.6606	$109.66	$109.65	$109.70
Purchase #7	$22.99	12.210%	$25.7971	$25.80	$25.80	$25.80
7 purchase totals =	$662.72		$712.9027	$712.91	$712.90	$713.00