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	$38.75	5.598%	$40.9192	$40.92	$40.90	$40.90
Purchase #2	$98.81	12.353%	$111.016	$111.02	$111.00	$111.00
Purchase #3	$193.92	12.698%	$218.544	$218.54	$218.55	$218.50
Purchase #4	$68.60	8.663%	$74.5428	$74.54	$74.55	$74.50
Purchase #5	$54.71	12.568%	$61.586	$61.59	$61.60	$61.60
Purchase #6	$194.63	8.214%	$210.6169	$210.62	$210.60	$210.60
Purchase #7	$50.67	5.121%	$53.2648	$53.26	$53.25	$53.30
7 purchase totals =	$700.09		$770.4897	$770.49	$770.45	$770.40