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	$170.47	9.718%	$187.0363	$187.04	$187.05	$187.00
Purchase #2	$248.74	4.157%	$259.0801	$259.08	$259.10	$259.10
Purchase #3	$29.92	5.277%	$31.4989	$31.50	$31.50	$31.50
Purchase #4	$155.40	5.704%	$164.264	$164.26	$164.25	$164.30
Purchase #5	$12.61	6.293%	$13.4035	$13.40	$13.40	$13.40
Purchase #6	$72.66	7.572%	$78.1618	$78.16	$78.15	$78.20
Purchase #7	$218.30	13.479%	$247.7247	$247.72	$247.70	$247.70
7 purchase totals =	$908.10		$981.1693	$981.16	$981.15	$981.20