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	$91.37	9.433%	$99.9889	$99.99	$100.00	$100.00
Purchase #2	$33.47	7.242%	$35.8939	$35.89	$35.90	$35.90
Purchase #3	$197.80	10.800%	$219.1624	$219.16	$219.15	$219.20
Purchase #4	$144.83	6.258%	$153.8935	$153.89	$153.90	$153.90
Purchase #5	$210.80	11.687%	$235.4362	$235.44	$235.45	$235.40
Purchase #6	$233.66	3.781%	$242.4947	$242.49	$242.50	$242.50
Purchase #7	$169.69	12.787%	$191.3883	$191.39	$191.40	$191.40
7 purchase totals =	$1,081.62		$1,178.2579	$1,178.25	$1,178.30	$1,178.30