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	$70.57	9.674%	$77.3969	$77.40	$77.40	$77.40
Purchase #2	$19.78	5.240%	$20.8165	$20.82	$20.80	$20.80
Purchase #3	$190.70	6.697%	$203.4712	$203.47	$203.45	$203.50
Purchase #4	$119.45	7.654%	$128.5927	$128.59	$128.60	$128.60
Purchase #5	$56.43	5.446%	$59.5032	$59.50	$59.50	$59.50
Purchase #6	$205.93	8.753%	$223.9551	$223.96	$223.95	$224.00
Purchase #7	$115.36	11.612%	$128.7556	$128.76	$128.75	$128.80
7 purchase totals =	$778.22		$842.4912	$842.50	$842.45	$842.60