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	$180.64	3.757%	$187.4266	$187.43	$187.45	$187.40
Purchase #2	$31.33	11.833%	$35.0373	$35.04	$35.05	$35.00
Purchase #3	$127.80	12.110%	$143.2766	$143.28	$143.30	$143.30
Purchase #4	$66.90	5.250%	$70.4123	$70.41	$70.40	$70.40
Purchase #5	$111.47	10.569%	$123.2513	$123.25	$123.25	$123.30
Purchase #6	$16.89	10.355%	$18.639	$18.64	$18.65	$18.60
Purchase #7	$194.93	12.582%	$219.4561	$219.46	$219.45	$219.50
7 purchase totals =	$729.96		$797.4992	$797.51	$797.55	$797.50