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	$243.58	6.403%	$259.1764	$259.18	$259.20	$259.20
Purchase #2	$160.56	11.109%	$178.3966	$178.40	$178.40	$178.40
Purchase #3	$26.50	7.721%	$28.5461	$28.55	$28.55	$28.50
Purchase #4	$158.42	10.223%	$174.6153	$174.62	$174.60	$174.60
Purchase #5	$85.71	13.322%	$97.1283	$97.13	$97.15	$97.10
Purchase #6	$137.90	11.340%	$153.5379	$153.54	$153.55	$153.50
Purchase #7	$229.34	13.326%	$259.9018	$259.90	$259.90	$259.90
7 purchase totals =	$1,042.01		$1,151.3024	$1,151.32	$1,151.35	$1,151.20