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	$155.72	3.721%	$161.5143	$161.51	$161.50	$161.50
Purchase #2	$220.77	12.836%	$249.108	$249.11	$249.10	$249.10
Purchase #3	$154.83	4.597%	$161.9475	$161.95	$161.95	$161.90
Purchase #4	$32.39	10.496%	$35.7897	$35.79	$35.80	$35.80
Purchase #5	$115.81	6.714%	$123.5855	$123.59	$123.60	$123.60
Purchase #6	$213.86	5.138%	$224.8481	$224.85	$224.85	$224.80
Purchase #7	$154.75	10.583%	$171.1272	$171.13	$171.15	$171.10
7 purchase totals =	$1,048.13		$1,127.9203	$1,127.93	$1,127.95	$1,127.80