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	$94.75	5.329%	$99.7992	$99.80	$99.80	$99.80
Purchase #2	$54.99	7.498%	$59.1132	$59.11	$59.10	$59.10
Purchase #3	$217.48	10.177%	$239.6129	$239.61	$239.60	$239.60
Purchase #4	$167.34	4.590%	$175.0209	$175.02	$175.00	$175.00
Purchase #5	$25.94	5.123%	$27.2689	$27.27	$27.25	$27.30
Purchase #6	$236.70	13.859%	$269.5043	$269.50	$269.50	$269.50
Purchase #7	$170.50	6.425%	$181.4546	$181.45	$181.45	$181.50
7 purchase totals =	$967.70		$1,051.7740	$1,051.76	$1,051.70	$1,051.80