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	$149.98	12.335%	$168.48	$168.48	$168.50	$168.50
Purchase #2	$118.52	11.249%	$131.8523	$131.85	$131.85	$131.90
Purchase #3	$101.63	4.559%	$106.2633	$106.26	$106.25	$106.30
Purchase #4	$89.48	6.190%	$95.0188	$95.02	$95.00	$95.00
Purchase #5	$49.90	7.867%	$53.8256	$53.83	$53.85	$53.80
Purchase #6	$25.55	6.269%	$27.1517	$27.15	$27.15	$27.20
Purchase #7	$225.59	5.305%	$237.5575	$237.56	$237.55	$237.60
7 purchase totals =	$760.65		$820.1492	$820.15	$820.15	$820.30