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	$122.89	11.811%	$137.4045	$137.40	$137.40	$137.40
Purchase #2	$79.60	11.867%	$89.0461	$89.05	$89.05	$89.00
Purchase #3	$9.54	10.770%	$10.5675	$10.57	$10.55	$10.60
Purchase #4	$72.30	11.841%	$80.861	$80.86	$80.85	$80.90
Purchase #5	$176.54	4.713%	$184.8603	$184.86	$184.85	$184.90
Purchase #6	$183.40	10.227%	$202.1563	$202.16	$202.15	$202.20
Purchase #7	$172.82	9.561%	$189.3433	$189.34	$189.35	$189.30
7 purchase totals =	$817.09		$894.2390	$894.24	$894.20	$894.30