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	$7.25	9.849%	$7.9641	$7.96	$7.95	$8.00
Purchase #2	$87.75	5.753%	$92.7983	$92.80	$92.80	$92.80
Purchase #3	$138.32	7.555%	$148.7701	$148.77	$148.75	$148.80
Purchase #4	$154.54	10.682%	$171.048	$171.05	$171.05	$171.00
Purchase #5	$98.70	12.612%	$111.148	$111.15	$111.15	$111.10
Purchase #6	$7.25	13.838%	$8.2533	$8.25	$8.25	$8.30
Purchase #7	$95.88	4.871%	$100.5503	$100.55	$100.55	$100.60
7 purchase totals =	$589.69		$640.5321	$640.53	$640.50	$640.60