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	$228.69	13.218%	$258.9182	$258.92	$258.90	$258.90
Purchase #2	$84.57	10.330%	$93.3061	$93.31	$93.30	$93.30
Purchase #3	$175.60	9.745%	$192.7122	$192.71	$192.70	$192.70
Purchase #4	$212.30	5.667%	$224.331	$224.33	$224.35	$224.30
Purchase #5	$104.26	7.322%	$111.8939	$111.89	$111.90	$111.90
Purchase #6	$37.56	8.598%	$40.7894	$40.79	$40.80	$40.80
Purchase #7	$161.98	4.247%	$168.8593	$168.86	$168.85	$168.90
7 purchase totals =	$1,004.96		$1,090.8101	$1,090.81	$1,090.80	$1,090.80