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	$101.46	11.215%	$112.8387	$112.84	$112.85	$112.80
Purchase #2	$180.42	3.239%	$186.2638	$186.26	$186.25	$186.30
Purchase #3	$54.81	12.108%	$61.4464	$61.45	$61.45	$61.40
Purchase #4	$225.92	10.286%	$249.1581	$249.16	$249.15	$249.20
Purchase #5	$55.62	6.399%	$59.1791	$59.18	$59.20	$59.20
Purchase #6	$77.67	9.547%	$85.0852	$85.09	$85.10	$85.10
Purchase #7	$160.89	4.536%	$168.188	$168.19	$168.20	$168.20
7 purchase totals =	$856.79		$922.1593	$922.17	$922.20	$922.20