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	$156.99	10.313%	$173.1804	$173.18	$173.20	$173.20
Purchase #2	$121.55	5.127%	$127.7819	$127.78	$127.80	$127.80
Purchase #3	$92.31	10.302%	$101.8198	$101.82	$101.80	$101.80
Purchase #4	$235.37	11.141%	$261.5926	$261.59	$261.60	$261.60
Purchase #5	$82.57	8.846%	$89.8741	$89.87	$89.85	$89.90
Purchase #6	$248.68	4.543%	$259.9775	$259.98	$260.00	$260.00
Purchase #7	$227.94	9.821%	$250.326	$250.33	$250.35	$250.30
7 purchase totals =	$1,165.41		$1,264.5523	$1,264.55	$1,264.60	$1,264.60