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	$20.58	6.550%	$21.928	$21.93	$21.95	$21.90
Purchase #2	$129.83	9.707%	$142.4326	$142.43	$142.45	$142.40
Purchase #3	$180.69	5.245%	$190.1672	$190.17	$190.15	$190.20
Purchase #4	$24.86	13.607%	$28.2427	$28.24	$28.25	$28.20
Purchase #5	$16.70	10.456%	$18.4462	$18.45	$18.45	$18.40
Purchase #6	$115.88	13.413%	$131.423	$131.42	$131.40	$131.40
Purchase #7	$16.96	7.606%	$18.25	$18.25	$18.25	$18.30
7 purchase totals =	$505.50		$550.8897	$550.89	$550.90	$550.80