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	$96.52	6.561%	$102.8527	$102.85	$102.85	$102.90
Purchase #2	$106.59	3.385%	$110.1981	$110.20	$110.20	$110.20
Purchase #3	$96.39	9.272%	$105.3273	$105.33	$105.35	$105.30
Purchase #4	$156.70	9.584%	$171.7181	$171.72	$171.70	$171.70
Purchase #5	$198.40	8.402%	$215.0696	$215.07	$215.05	$215.10
Purchase #6	$65.42	10.322%	$72.1727	$72.17	$72.15	$72.20
Purchase #7	$35.60	7.570%	$38.2949	$38.29	$38.30	$38.30
7 purchase totals =	$755.62		$815.6334	$815.63	$815.60	$815.70