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	$123.93	12.325%	$139.2044	$139.20	$139.20	$139.20
Purchase #2	$145.52	10.156%	$160.299	$160.30	$160.30	$160.30
Purchase #3	$156.97	5.365%	$165.3914	$165.39	$165.40	$165.40
Purchase #4	$142.91	13.693%	$162.4787	$162.48	$162.50	$162.50
Purchase #5	$5.52	7.329%	$5.9246	$5.92	$5.90	$5.90
Purchase #6	$84.96	11.278%	$94.5418	$94.54	$94.55	$94.50
Purchase #7	$160.68	4.420%	$167.7821	$167.78	$167.80	$167.80
7 purchase totals =	$820.49		$895.6220	$895.61	$895.65	$895.60