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	$53.77	6.874%	$57.4661	$57.47	$57.45	$57.50
Purchase #2	$37.96	11.506%	$42.3277	$42.33	$42.35	$42.30
Purchase #3	$65.35	12.314%	$73.3972	$73.40	$73.40	$73.40
Purchase #4	$158.27	7.145%	$169.5784	$169.58	$169.60	$169.60
Purchase #5	$97.44	4.262%	$101.5929	$101.59	$101.60	$101.60
Purchase #6	$83.52	4.661%	$87.4129	$87.41	$87.40	$87.40
Purchase #7	$114.92	11.456%	$128.0852	$128.09	$128.10	$128.10
7 purchase totals =	$611.23		$659.8604	$659.87	$659.90	$659.90