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	$33.83	7.846%	$36.4843	$36.48	$36.50	$36.50
Purchase #2	$148.57	9.420%	$162.5653	$162.57	$162.55	$162.60
Purchase #3	$229.38	10.654%	$253.8181	$253.82	$253.80	$253.80
Purchase #4	$98.28	3.268%	$101.4918	$101.49	$101.50	$101.50
Purchase #5	$48.94	10.441%	$54.0498	$54.05	$54.05	$54.00
Purchase #6	$210.33	7.315%	$225.7156	$225.72	$225.70	$225.70
Purchase #7	$59.31	12.583%	$66.773	$66.77	$66.75	$66.80
7 purchase totals =	$828.64		$900.8979	$900.90	$900.85	$900.90