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	$53.43	10.564%	$59.0743	$59.07	$59.05	$59.10
Purchase #2	$31.97	9.765%	$35.0919	$35.09	$35.10	$35.10
Purchase #3	$117.43	9.591%	$128.6927	$128.69	$128.70	$128.70
Purchase #4	$225.28	11.266%	$250.66	$250.66	$250.65	$250.70
Purchase #5	$80.29	11.373%	$89.4214	$89.42	$89.40	$89.40
Purchase #6	$139.88	3.420%	$144.6639	$144.66	$144.65	$144.70
Purchase #7	$238.71	10.272%	$263.2303	$263.23	$263.25	$263.20
7 purchase totals =	$886.99		$970.8345	$970.82	$970.80	$970.90