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	$224.43	12.828%	$253.2199	$253.22	$253.20	$253.20
Purchase #2	$108.69	13.455%	$123.3142	$123.31	$123.30	$123.30
Purchase #3	$99.32	6.854%	$106.1274	$106.13	$106.15	$106.10
Purchase #4	$218.67	10.275%	$241.1383	$241.14	$241.15	$241.10
Purchase #5	$218.86	4.697%	$229.1399	$229.14	$229.15	$229.10
Purchase #6	$132.86	12.398%	$149.332	$149.33	$149.35	$149.30
Purchase #7	$124.27	13.159%	$140.6227	$140.62	$140.60	$140.60
7 purchase totals =	$1,127.10		$1,242.8944	$1,242.89	$1,242.90	$1,242.70