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	$157.52	3.515%	$163.0568	$163.06	$163.05	$163.10
Purchase #2	$174.52	12.759%	$196.787	$196.79	$196.80	$196.80
Purchase #3	$78.66	13.253%	$89.0848	$89.08	$89.10	$89.10
Purchase #4	$112.47	10.692%	$124.4953	$124.50	$124.50	$124.50
Purchase #5	$35.55	7.549%	$38.2337	$38.23	$38.25	$38.20
Purchase #6	$75.87	13.484%	$86.1003	$86.10	$86.10	$86.10
Purchase #7	$143.52	10.720%	$158.9053	$158.91	$158.90	$158.90
7 purchase totals =	$778.11		$856.6632	$856.67	$856.70	$856.70