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	$178.76	6.277%	$189.9808	$189.98	$190.00	$190.00
Purchase #2	$210.76	9.708%	$231.2206	$231.22	$231.20	$231.20
Purchase #3	$249.70	12.776%	$281.6017	$281.60	$281.60	$281.60
Purchase #4	$118.58	6.641%	$126.4549	$126.45	$126.45	$126.50
Purchase #5	$172.99	13.743%	$196.764	$196.76	$196.75	$196.80
Purchase #6	$97.58	10.494%	$107.82	$107.82	$107.80	$107.80
Purchase #7	$156.28	7.241%	$167.5962	$167.60	$167.60	$167.60
7 purchase totals =	$1,184.65		$1,301.4382	$1,301.43	$1,301.40	$1,301.50