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	$108.69	13.390%	$123.2436	$123.24	$123.25	$123.20
Purchase #2	$161.43	4.580%	$168.8235	$168.82	$168.80	$168.80
Purchase #3	$232.35	10.523%	$256.8002	$256.80	$256.80	$256.80
Purchase #4	$194.28	13.165%	$219.857	$219.86	$219.85	$219.90
Purchase #5	$56.49	4.533%	$59.0507	$59.05	$59.05	$59.10
Purchase #6	$74.67	9.489%	$81.7554	$81.76	$81.75	$81.80
Purchase #7	$38.71	5.414%	$40.8058	$40.81	$40.80	$40.80
7 purchase totals =	$866.62		$950.3362	$950.34	$950.30	$950.40