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	$25.66	3.370%	$26.5247	$26.52	$26.50	$26.50
Purchase #2	$164.60	4.860%	$172.5996	$172.60	$172.60	$172.60
Purchase #3	$243.72	9.592%	$267.0976	$267.10	$267.10	$267.10
Purchase #4	$212.36	6.245%	$225.6219	$225.62	$225.60	$225.60
Purchase #5	$75.53	9.461%	$82.6759	$82.68	$82.70	$82.70
Purchase #6	$214.34	5.241%	$225.5736	$225.57	$225.55	$225.60
Purchase #7	$64.61	11.796%	$72.2314	$72.23	$72.25	$72.20
7 purchase totals =	$1,000.82		$1,072.3247	$1,072.32	$1,072.30	$1,072.30