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	$115.82	3.751%	$120.1644	$120.16	$120.15	$120.20
Purchase #2	$31.43	12.700%	$35.4216	$35.42	$35.40	$35.40
Purchase #3	$151.30	13.838%	$172.2369	$172.24	$172.25	$172.20
Purchase #4	$6.43	13.606%	$7.3049	$7.30	$7.30	$7.30
Purchase #5	$95.39	12.256%	$107.081	$107.08	$107.10	$107.10
Purchase #6	$83.80	7.266%	$89.8889	$89.89	$89.90	$89.90
Purchase #7	$230.59	11.715%	$257.6036	$257.60	$257.60	$257.60
7 purchase totals =	$714.76		$789.7013	$789.69	$789.70	$789.70