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	$38.95	4.696%	$40.7791	$40.78	$40.80	$40.80
Purchase #2	$156.28	5.757%	$165.277	$165.28	$165.30	$165.30
Purchase #3	$82.62	8.224%	$89.4147	$89.41	$89.40	$89.40
Purchase #4	$199.46	5.213%	$209.8578	$209.86	$209.85	$209.90
Purchase #5	$163.55	10.831%	$181.2641	$181.26	$181.25	$181.30
Purchase #6	$10.85	6.786%	$11.5863	$11.59	$11.60	$11.60
Purchase #7	$77.35	10.636%	$85.5769	$85.58	$85.60	$85.60
7 purchase totals =	$729.06		$783.7559	$783.76	$783.80	$783.90