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	$240.43	3.714%	$249.3596	$249.36	$249.35	$249.40
Purchase #2	$159.55	7.366%	$171.3025	$171.30	$171.30	$171.30
Purchase #3	$105.89	5.812%	$112.0443	$112.04	$112.05	$112.00
Purchase #4	$14.48	8.207%	$15.6684	$15.67	$15.65	$15.70
Purchase #5	$122.46	7.611%	$131.7804	$131.78	$131.80	$131.80
Purchase #6	$127.71	9.229%	$139.4964	$139.50	$139.50	$139.50
Purchase #7	$61.62	9.690%	$67.591	$67.59	$67.60	$67.60
7 purchase totals =	$832.14		$887.2426	$887.24	$887.25	$887.30