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	$222.53	10.139%	$245.0923	$245.09	$245.10	$245.10
Purchase #2	$31.88	7.448%	$34.2544	$34.25	$34.25	$34.30
Purchase #3	$103.69	11.850%	$115.9773	$115.98	$116.00	$116.00
Purchase #4	$240.54	4.296%	$250.8736	$250.87	$250.85	$250.90
Purchase #5	$83.97	13.622%	$95.4084	$95.41	$95.40	$95.40
Purchase #6	$42.79	5.702%	$45.2299	$45.23	$45.25	$45.20
Purchase #7	$85.48	5.292%	$90.0036	$90.00	$90.00	$90.00
7 purchase totals =	$810.88		$876.8395	$876.83	$876.85	$876.90