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	$80.94	3.379%	$83.675	$83.68	$83.70	$83.70
Purchase #2	$128.95	7.841%	$139.061	$139.06	$139.05	$139.10
Purchase #3	$41.37	3.790%	$42.9379	$42.94	$42.95	$42.90
Purchase #4	$68.66	5.764%	$72.6176	$72.62	$72.60	$72.60
Purchase #5	$134.30	7.859%	$144.8546	$144.85	$144.85	$144.90
Purchase #6	$206.80	8.657%	$224.7027	$224.70	$224.70	$224.70
Purchase #7	$80.71	5.852%	$85.4331	$85.43	$85.45	$85.40
7 purchase totals =	$741.73		$793.2819	$793.28	$793.30	$793.30