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	$69.83	6.667%	$74.4856	$74.49	$74.50	$74.50
Purchase #2	$215.74	3.441%	$223.1636	$223.16	$223.15	$223.20
Purchase #3	$168.46	12.128%	$188.8908	$188.89	$188.90	$188.90
Purchase #4	$44.59	9.179%	$48.6829	$48.68	$48.70	$48.70
Purchase #5	$224.43	5.573%	$236.9375	$236.94	$236.95	$236.90
Purchase #6	$48.93	4.757%	$51.2576	$51.26	$51.25	$51.30
Purchase #7	$80.73	10.515%	$89.2188	$89.22	$89.20	$89.20
7 purchase totals =	$852.71		$912.6368	$912.64	$912.65	$912.70