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	$220.50	8.693%	$239.6681	$239.67	$239.65	$239.70
Purchase #2	$53.86	9.746%	$59.1092	$59.11	$59.10	$59.10
Purchase #3	$88.41	3.572%	$91.568	$91.57	$91.55	$91.60
Purchase #4	$206.94	12.376%	$232.5509	$232.55	$232.55	$232.60
Purchase #5	$108.80	3.298%	$112.3882	$112.39	$112.40	$112.40
Purchase #6	$52.61	12.593%	$59.2352	$59.24	$59.25	$59.20
Purchase #7	$209.70	12.594%	$236.1096	$236.11	$236.10	$236.10
7 purchase totals =	$940.82		$1,030.6292	$1,030.64	$1,030.60	$1,030.70