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	$73.82	6.336%	$78.4972	$78.50	$78.50	$78.50
Purchase #2	$98.89	4.849%	$103.6852	$103.69	$103.70	$103.70
Purchase #3	$48.54	11.374%	$54.0609	$54.06	$54.05	$54.10
Purchase #4	$71.98	10.390%	$79.4587	$79.46	$79.45	$79.50
Purchase #5	$192.60	3.441%	$199.2274	$199.23	$199.25	$199.20
Purchase #6	$109.87	8.187%	$118.8651	$118.87	$118.85	$118.90
Purchase #7	$28.98	9.672%	$31.7829	$31.78	$31.80	$31.80
7 purchase totals =	$624.68		$665.5774	$665.59	$665.60	$665.70