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	$40.29	4.523%	$42.1123	$42.11	$42.10	$42.10
Purchase #2	$224.90	8.862%	$244.8306	$244.83	$244.85	$244.80
Purchase #3	$167.69	8.641%	$182.1801	$182.18	$182.20	$182.20
Purchase #4	$210.81	6.342%	$224.1796	$224.18	$224.20	$224.20
Purchase #5	$124.92	10.442%	$137.9641	$137.96	$137.95	$138.00
Purchase #6	$245.48	12.200%	$275.4286	$275.43	$275.45	$275.40
Purchase #7	$225.46	13.364%	$255.5905	$255.59	$255.60	$255.60
7 purchase totals =	$1,239.55		$1,362.2858	$1,362.28	$1,362.35	$1,362.30