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	$37.44	13.582%	$42.5251	$42.53	$42.55	$42.50
Purchase #2	$19.56	5.124%	$20.5623	$20.56	$20.55	$20.60
Purchase #3	$189.33	11.873%	$211.8092	$211.81	$211.80	$211.80
Purchase #4	$43.51	10.518%	$48.0864	$48.09	$48.10	$48.10
Purchase #5	$209.56	4.539%	$219.0719	$219.07	$219.05	$219.10
Purchase #6	$59.81	5.451%	$63.0702	$63.07	$63.05	$63.10
Purchase #7	$164.54	12.481%	$185.0762	$185.08	$185.10	$185.10
7 purchase totals =	$723.75		$790.2013	$790.21	$790.20	$790.30