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	$88.91	12.394%	$99.9295	$99.93	$99.95	$99.90
Purchase #2	$36.50	3.754%	$37.8702	$37.87	$37.85	$37.90
Purchase #3	$108.40	10.148%	$119.4004	$119.40	$119.40	$119.40
Purchase #4	$93.52	10.133%	$102.9964	$103.00	$103.00	$103.00
Purchase #5	$202.93	13.487%	$230.2992	$230.30	$230.30	$230.30
Purchase #6	$61.48	5.174%	$64.661	$64.66	$64.65	$64.70
Purchase #7	$30.64	12.222%	$34.3848	$34.38	$34.40	$34.40
7 purchase totals =	$622.38		$689.5415	$689.54	$689.55	$689.60