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	$71.79	7.657%	$77.287	$77.29	$77.30	$77.30
Purchase #2	$111.74	11.515%	$124.6069	$124.61	$124.60	$124.60
Purchase #3	$228.59	4.502%	$238.8811	$238.88	$238.90	$238.90
Purchase #4	$65.33	8.282%	$70.7406	$70.74	$70.75	$70.70
Purchase #5	$207.69	10.667%	$229.8443	$229.84	$229.85	$229.80
Purchase #6	$162.27	5.873%	$171.8001	$171.80	$171.80	$171.80
Purchase #7	$78.81	9.661%	$86.4238	$86.42	$86.40	$86.40
7 purchase totals =	$926.22		$999.5838	$999.58	$999.60	$999.50