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	$110.39	6.801%	$117.8976	$117.90	$117.90	$117.90
Purchase #2	$86.56	5.776%	$91.5597	$91.56	$91.55	$91.60
Purchase #3	$107.45	5.231%	$113.0707	$113.07	$113.05	$113.10
Purchase #4	$91.92	12.643%	$103.5414	$103.54	$103.55	$103.50
Purchase #5	$69.31	13.335%	$78.5525	$78.55	$78.55	$78.60
Purchase #6	$179.88	10.623%	$198.9887	$198.99	$199.00	$199.00
Purchase #7	$24.45	13.556%	$27.7644	$27.76	$27.75	$27.80
7 purchase totals =	$669.96		$731.3750	$731.37	$731.35	$731.50