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	$38.62	10.593%	$42.711	$42.71	$42.70	$42.70
Purchase #2	$18.96	7.528%	$20.3873	$20.39	$20.40	$20.40
Purchase #3	$79.77	4.445%	$83.3158	$83.32	$83.30	$83.30
Purchase #4	$140.82	5.577%	$148.6735	$148.67	$148.65	$148.70
Purchase #5	$167.64	6.670%	$178.8216	$178.82	$178.80	$178.80
Purchase #6	$164.69	8.392%	$178.5108	$178.51	$178.50	$178.50
Purchase #7	$26.48	7.867%	$28.5632	$28.56	$28.55	$28.60
7 purchase totals =	$636.98		$680.9832	$680.98	$680.90	$681.00