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	$73.61	3.238%	$75.9935	$75.99	$76.00	$76.00
Purchase #2	$143.55	12.211%	$161.0789	$161.08	$161.10	$161.10
Purchase #3	$159.43	3.613%	$165.1902	$165.19	$165.20	$165.20
Purchase #4	$111.98	6.849%	$119.6495	$119.65	$119.65	$119.60
Purchase #5	$83.33	7.798%	$89.8281	$89.83	$89.85	$89.80
Purchase #6	$161.91	10.730%	$179.2829	$179.28	$179.30	$179.30
Purchase #7	$85.92	3.835%	$89.215	$89.22	$89.20	$89.20
7 purchase totals =	$819.73		$880.2381	$880.24	$880.30	$880.20