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	$137.25	9.196%	$149.8715	$149.87	$149.85	$149.90
Purchase #2	$192.52	10.556%	$212.8424	$212.84	$212.85	$212.80
Purchase #3	$236.68	11.818%	$264.6508	$264.65	$264.65	$264.70
Purchase #4	$36.55	4.782%	$38.2978	$38.30	$38.30	$38.30
Purchase #5	$84.27	6.583%	$89.8175	$89.82	$89.80	$89.80
Purchase #6	$172.89	3.500%	$178.9412	$178.94	$178.95	$178.90
Purchase #7	$226.87	13.154%	$256.7125	$256.71	$256.70	$256.70
7 purchase totals =	$1,087.03		$1,191.1337	$1,191.13	$1,191.10	$1,191.10