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	$47.51	12.254%	$53.3319	$53.33	$53.35	$53.30
Purchase #2	$116.43	10.700%	$128.888	$128.89	$128.90	$128.90
Purchase #3	$13.76	13.543%	$15.6235	$15.62	$15.60	$15.60
Purchase #4	$149.45	8.737%	$162.5074	$162.51	$162.50	$162.50
Purchase #5	$56.43	12.688%	$63.5898	$63.59	$63.60	$63.60
Purchase #6	$68.89	13.211%	$77.9911	$77.99	$78.00	$78.00
Purchase #7	$222.33	4.180%	$231.6234	$231.62	$231.60	$231.60
7 purchase totals =	$674.80		$733.5551	$733.55	$733.55	$733.50