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	$30.52	4.176%	$31.7945	$31.79	$31.80	$31.80
Purchase #2	$33.96	10.486%	$37.521	$37.52	$37.50	$37.50
Purchase #3	$154.97	6.864%	$165.6071	$165.61	$165.60	$165.60
Purchase #4	$89.25	3.722%	$92.5719	$92.57	$92.55	$92.60
Purchase #5	$175.53	9.591%	$192.3651	$192.37	$192.35	$192.40
Purchase #6	$32.49	9.104%	$35.4479	$35.45	$35.45	$35.40
Purchase #7	$113.64	3.684%	$117.8265	$117.83	$117.85	$117.80
7 purchase totals =	$630.36		$673.1340	$673.14	$673.10	$673.10