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	$217.64	10.675%	$240.8731	$240.87	$240.85	$240.90
Purchase #2	$85.91	5.286%	$90.4512	$90.45	$90.45	$90.50
Purchase #3	$195.88	13.216%	$221.7675	$221.77	$221.75	$221.80
Purchase #4	$135.59	6.350%	$144.2	$144.20	$144.20	$144.20
Purchase #5	$39.96	6.329%	$42.4891	$42.49	$42.50	$42.50
Purchase #6	$46.42	7.108%	$49.7195	$49.72	$49.70	$49.70
Purchase #7	$73.82	10.134%	$81.3009	$81.30	$81.30	$81.30
7 purchase totals =	$795.22		$870.8013	$870.80	$870.75	$870.90