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	$66.59	9.471%	$72.8967	$72.90	$72.90	$72.90
Purchase #2	$20.83	5.441%	$21.9634	$21.96	$21.95	$22.00
Purchase #3	$95.55	10.470%	$105.5541	$105.55	$105.55	$105.60
Purchase #4	$106.46	6.773%	$113.6705	$113.67	$113.65	$113.70
Purchase #5	$20.54	5.722%	$21.7153	$21.72	$21.70	$21.70
Purchase #6	$93.33	12.594%	$105.084	$105.08	$105.10	$105.10
Purchase #7	$99.38	9.133%	$108.4564	$108.46	$108.45	$108.50
7 purchase totals =	$502.68		$549.3404	$549.34	$549.30	$549.50