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	$229.37	5.653%	$242.3363	$242.34	$242.35	$242.30
Purchase #2	$139.83	9.639%	$153.3082	$153.31	$153.30	$153.30
Purchase #3	$132.40	10.459%	$146.2477	$146.25	$146.25	$146.20
Purchase #4	$37.59	13.836%	$42.791	$42.79	$42.80	$42.80
Purchase #5	$45.38	13.465%	$51.4904	$51.49	$51.50	$51.50
Purchase #6	$125.42	13.348%	$142.1611	$142.16	$142.15	$142.20
Purchase #7	$79.46	13.386%	$90.0965	$90.10	$90.10	$90.10
7 purchase totals =	$789.45		$868.4312	$868.44	$868.45	$868.40