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	$33.35	10.265%	$36.7734	$36.77	$36.75	$36.80
Purchase #2	$134.71	11.587%	$150.3188	$150.32	$150.30	$150.30
Purchase #3	$6.65	10.224%	$7.3299	$7.33	$7.35	$7.30
Purchase #4	$167.40	3.379%	$173.0564	$173.06	$173.05	$173.10
Purchase #5	$172.25	10.646%	$190.5877	$190.59	$190.60	$190.60
Purchase #6	$171.90	5.122%	$180.7047	$180.70	$180.70	$180.70
Purchase #7	$38.43	4.204%	$40.0456	$40.05	$40.05	$40.00
7 purchase totals =	$724.69		$778.8165	$778.82	$778.80	$778.80