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	$235.36	12.283%	$264.2693	$264.27	$264.25	$264.30
Purchase #2	$226.95	9.405%	$248.2946	$248.29	$248.30	$248.30
Purchase #3	$35.71	5.796%	$37.7798	$37.78	$37.80	$37.80
Purchase #4	$231.55	6.711%	$247.0893	$247.09	$247.10	$247.10
Purchase #5	$185.59	13.340%	$210.3477	$210.35	$210.35	$210.30
Purchase #6	$37.95	12.838%	$42.822	$42.82	$42.80	$42.80
Purchase #7	$228.59	12.858%	$257.9821	$257.98	$258.00	$258.00
7 purchase totals =	$1,181.70		$1,308.5848	$1,308.58	$1,308.60	$1,308.60