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	$24.55	12.142%	$27.5309	$27.53	$27.55	$27.50
Purchase #2	$217.34	13.543%	$246.7744	$246.77	$246.75	$246.80
Purchase #3	$81.59	9.871%	$89.6437	$89.64	$89.65	$89.60
Purchase #4	$212.59	10.123%	$234.1105	$234.11	$234.10	$234.10
Purchase #5	$224.50	4.440%	$234.4678	$234.47	$234.45	$234.50
Purchase #6	$29.77	10.275%	$32.8289	$32.83	$32.85	$32.80
Purchase #7	$76.56	3.738%	$79.4218	$79.42	$79.40	$79.40
7 purchase totals =	$866.90		$944.7780	$944.77	$944.75	$944.70