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	$141.38	3.398%	$146.1841	$146.18	$146.20	$146.20
Purchase #2	$98.98	4.680%	$103.6123	$103.61	$103.60	$103.60
Purchase #3	$21.59	13.821%	$24.574	$24.57	$24.55	$24.60
Purchase #4	$90.84	4.556%	$94.9787	$94.98	$95.00	$95.00
Purchase #5	$37.88	7.765%	$40.8214	$40.82	$40.80	$40.80
Purchase #6	$168.60	8.159%	$182.3561	$182.36	$182.35	$182.40
Purchase #7	$45.45	6.746%	$48.5161	$48.52	$48.50	$48.50
7 purchase totals =	$604.72		$641.0427	$641.04	$641.00	$641.10