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	$128.77	13.853%	$146.6085	$146.61	$146.60	$146.60
Purchase #2	$216.53	5.441%	$228.3114	$228.31	$228.30	$228.30
Purchase #3	$98.27	7.761%	$105.8967	$105.90	$105.90	$105.90
Purchase #4	$9.82	9.503%	$10.7532	$10.75	$10.75	$10.80
Purchase #5	$99.81	3.864%	$103.6667	$103.67	$103.65	$103.70
Purchase #6	$246.39	13.649%	$280.0198	$280.02	$280.00	$280.00
Purchase #7	$79.92	12.610%	$89.9979	$90.00	$90.00	$90.00
7 purchase totals =	$879.51		$965.2542	$965.26	$965.20	$965.30