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	$212.38	9.302%	$232.1356	$232.14	$232.15	$232.10
Purchase #2	$139.83	3.256%	$144.3829	$144.38	$144.40	$144.40
Purchase #3	$103.54	8.143%	$111.9713	$111.97	$111.95	$112.00
Purchase #4	$34.96	12.487%	$39.3255	$39.33	$39.35	$39.30
Purchase #5	$166.28	11.442%	$185.3058	$185.31	$185.30	$185.30
Purchase #6	$161.37	9.235%	$176.2725	$176.27	$176.25	$176.30
Purchase #7	$31.59	13.380%	$35.8167	$35.82	$35.80	$35.80
7 purchase totals =	$849.95		$925.2103	$925.22	$925.20	$925.20