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	$179.48	13.712%	$204.0903	$204.09	$204.10	$204.10
Purchase #2	$242.26	11.712%	$270.6335	$270.63	$270.65	$270.60
Purchase #3	$35.87	4.293%	$37.4099	$37.41	$37.40	$37.40
Purchase #4	$166.81	11.436%	$185.8864	$185.89	$185.90	$185.90
Purchase #5	$19.44	8.743%	$21.1396	$21.14	$21.15	$21.10
Purchase #6	$62.65	4.119%	$65.2306	$65.23	$65.25	$65.20
Purchase #7	$51.82	4.246%	$54.0203	$54.02	$54.00	$54.00
7 purchase totals =	$758.33		$838.4106	$838.41	$838.45	$838.30