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	$88.91	13.664%	$101.0587	$101.06	$101.05	$101.10
Purchase #2	$127.27	3.392%	$131.587	$131.59	$131.60	$131.60
Purchase #3	$176.28	5.439%	$185.8679	$185.87	$185.85	$185.90
Purchase #4	$243.77	13.569%	$276.8472	$276.85	$276.85	$276.80
Purchase #5	$83.26	5.730%	$88.0308	$88.03	$88.05	$88.00
Purchase #6	$6.93	4.858%	$7.2667	$7.27	$7.25	$7.30
Purchase #7	$27.88	11.337%	$31.0408	$31.04	$31.05	$31.00
7 purchase totals =	$754.30		$821.6991	$821.71	$821.70	$821.70