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	$104.36	6.244%	$110.8762	$110.88	$110.90	$110.90
Purchase #2	$247.53	4.818%	$259.456	$259.46	$259.45	$259.50
Purchase #3	$113.47	4.421%	$118.4865	$118.49	$118.50	$118.50
Purchase #4	$94.36	5.379%	$99.4356	$99.44	$99.45	$99.40
Purchase #5	$90.45	10.698%	$100.1263	$100.13	$100.15	$100.10
Purchase #6	$43.69	3.360%	$45.158	$45.16	$45.15	$45.20
Purchase #7	$134.57	10.868%	$149.1951	$149.20	$149.20	$149.20
7 purchase totals =	$828.43		$882.7337	$882.76	$882.80	$882.80