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	$52.59	5.124%	$55.2847	$55.28	$55.30	$55.30
Purchase #2	$82.28	7.254%	$88.2486	$88.25	$88.25	$88.20
Purchase #3	$137.79	5.169%	$144.9124	$144.91	$144.90	$144.90
Purchase #4	$221.36	7.704%	$238.4136	$238.41	$238.40	$238.40
Purchase #5	$197.82	12.734%	$223.0104	$223.01	$223.00	$223.00
Purchase #6	$58.54	13.814%	$66.6267	$66.63	$66.65	$66.60
Purchase #7	$175.34	9.569%	$192.1183	$192.12	$192.10	$192.10
7 purchase totals =	$925.72		$1,008.6147	$1,008.61	$1,008.60	$1,008.50