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	$71.58	9.763%	$78.5684	$78.57	$78.55	$78.60
Purchase #2	$30.70	9.373%	$33.5775	$33.58	$33.60	$33.60
Purchase #3	$78.65	8.505%	$85.3392	$85.34	$85.35	$85.30
Purchase #4	$152.44	10.602%	$168.6017	$168.60	$168.60	$168.60
Purchase #5	$71.39	13.596%	$81.0962	$81.10	$81.10	$81.10
Purchase #6	$239.91	5.619%	$253.3905	$253.39	$253.40	$253.40
Purchase #7	$98.97	3.790%	$102.721	$102.72	$102.70	$102.70
7 purchase totals =	$743.64		$803.2945	$803.30	$803.30	$803.30