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	$19.38	12.745%	$21.85	$21.85	$21.85	$21.90
Purchase #2	$90.31	4.124%	$94.0344	$94.03	$94.05	$94.00
Purchase #3	$164.98	13.695%	$187.574	$187.57	$187.55	$187.60
Purchase #4	$91.86	9.225%	$100.3341	$100.33	$100.35	$100.30
Purchase #5	$244.86	3.338%	$253.0334	$253.03	$253.05	$253.00
Purchase #6	$172.50	11.465%	$192.2771	$192.28	$192.30	$192.30
Purchase #7	$141.37	9.428%	$154.6984	$154.70	$154.70	$154.70
7 purchase totals =	$925.26		$1,003.8014	$1,003.79	$1,003.85	$1,003.80