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	$56.99	7.231%	$61.1109	$61.11	$61.10	$61.10
Purchase #2	$44.93	13.718%	$51.0935	$51.09	$51.10	$51.10
Purchase #3	$86.60	3.386%	$89.5323	$89.53	$89.55	$89.50
Purchase #4	$202.27	3.559%	$209.4688	$209.47	$209.45	$209.50
Purchase #5	$146.55	7.486%	$157.5207	$157.52	$157.50	$157.50
Purchase #6	$114.81	8.387%	$124.4391	$124.44	$124.45	$124.40
Purchase #7	$61.67	12.637%	$69.4632	$69.46	$69.45	$69.50
7 purchase totals =	$713.82		$762.6285	$762.62	$762.60	$762.60