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	$160.91	12.827%	$181.5499	$181.55	$181.55	$181.50
Purchase #2	$72.51	11.642%	$80.9516	$80.95	$80.95	$81.00
Purchase #3	$85.70	5.174%	$90.1341	$90.13	$90.15	$90.10
Purchase #4	$245.31	3.341%	$253.5058	$253.51	$253.50	$253.50
Purchase #5	$110.76	5.291%	$116.6203	$116.62	$116.60	$116.60
Purchase #6	$93.30	5.156%	$98.1105	$98.11	$98.10	$98.10
Purchase #7	$26.25	10.150%	$28.9144	$28.91	$28.90	$28.90
7 purchase totals =	$794.74		$849.7866	$849.78	$849.75	$849.70