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	$209.57	13.712%	$238.3062	$238.31	$238.30	$238.30
Purchase #2	$149.70	4.778%	$156.8527	$156.85	$156.85	$156.90
Purchase #3	$165.76	10.174%	$182.6244	$182.62	$182.60	$182.60
Purchase #4	$54.27	9.457%	$59.4023	$59.40	$59.40	$59.40
Purchase #5	$113.61	12.782%	$128.1316	$128.13	$128.15	$128.10
Purchase #6	$240.75	10.584%	$266.231	$266.23	$266.25	$266.20
Purchase #7	$51.38	13.206%	$58.1652	$58.17	$58.15	$58.20
7 purchase totals =	$985.04		$1,089.7134	$1,089.71	$1,089.70	$1,089.70