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	$198.56	9.224%	$216.8752	$216.88	$216.90	$216.90
Purchase #2	$217.77	10.420%	$240.4616	$240.46	$240.45	$240.50
Purchase #3	$172.83	10.227%	$190.5053	$190.51	$190.50	$190.50
Purchase #4	$30.77	3.397%	$31.8153	$31.82	$31.80	$31.80
Purchase #5	$244.37	10.729%	$270.5885	$270.59	$270.60	$270.60
Purchase #6	$197.64	9.345%	$216.1095	$216.11	$216.10	$216.10
Purchase #7	$200.27	11.690%	$223.6816	$223.68	$223.70	$223.70
7 purchase totals =	$1,262.21		$1,390.0370	$1,390.05	$1,390.05	$1,390.10