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	$80.70	10.318%	$89.0266	$89.03	$89.05	$89.00
Purchase #2	$100.70	12.542%	$113.3298	$113.33	$113.35	$113.30
Purchase #3	$42.28	7.635%	$45.5081	$45.51	$45.50	$45.50
Purchase #4	$120.81	4.636%	$126.4108	$126.41	$126.40	$126.40
Purchase #5	$123.67	3.648%	$128.1815	$128.18	$128.20	$128.20
Purchase #6	$44.51	6.316%	$47.3213	$47.32	$47.30	$47.30
Purchase #7	$248.91	4.671%	$260.5366	$260.54	$260.55	$260.50
7 purchase totals =	$761.58		$810.3147	$810.32	$810.35	$810.20