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	$165.63	6.483%	$176.3678	$176.37	$176.35	$176.40
Purchase #2	$162.80	8.368%	$176.4231	$176.42	$176.40	$176.40
Purchase #3	$52.64	3.765%	$54.6219	$54.62	$54.60	$54.60
Purchase #4	$106.39	9.858%	$116.8779	$116.88	$116.90	$116.90
Purchase #5	$37.60	12.437%	$42.2763	$42.28	$42.30	$42.30
Purchase #6	$134.99	3.218%	$139.334	$139.33	$139.35	$139.30
Purchase #7	$119.31	3.412%	$123.3809	$123.38	$123.40	$123.40
7 purchase totals =	$779.36		$829.2819	$829.28	$829.30	$829.30