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	$34.56	10.751%	$38.2755	$38.28	$38.30	$38.30
Purchase #2	$96.77	5.309%	$101.9075	$101.91	$101.90	$101.90
Purchase #3	$111.84	9.799%	$122.7992	$122.80	$122.80	$122.80
Purchase #4	$109.85	9.253%	$120.0144	$120.01	$120.00	$120.00
Purchase #5	$85.67	5.395%	$90.2919	$90.29	$90.30	$90.30
Purchase #6	$168.69	13.109%	$190.8036	$190.80	$190.80	$190.80
Purchase #7	$59.36	5.562%	$62.6616	$62.66	$62.65	$62.70
7 purchase totals =	$666.74		$726.7537	$726.75	$726.75	$726.80