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	$246.52	4.434%	$257.4507	$257.45	$257.45	$257.50
Purchase #2	$71.45	9.484%	$78.2263	$78.23	$78.25	$78.20
Purchase #3	$52.33	4.242%	$54.5498	$54.55	$54.55	$54.50
Purchase #4	$39.87	7.538%	$42.8754	$42.88	$42.90	$42.90
Purchase #5	$59.48	13.141%	$67.2963	$67.30	$67.30	$67.30
Purchase #6	$92.43	3.383%	$95.5569	$95.56	$95.55	$95.60
Purchase #7	$176.73	6.451%	$188.1309	$188.13	$188.15	$188.10
7 purchase totals =	$738.81		$784.0863	$784.10	$784.15	$784.10