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	$31.67	7.681%	$34.1026	$34.10	$34.10	$34.10
Purchase #2	$92.35	9.734%	$101.3393	$101.34	$101.35	$101.30
Purchase #3	$57.26	3.235%	$59.1124	$59.11	$59.10	$59.10
Purchase #4	$154.69	8.326%	$167.5695	$167.57	$167.55	$167.60
Purchase #5	$35.97	7.734%	$38.7519	$38.75	$38.75	$38.80
Purchase #6	$58.25	5.249%	$61.3075	$61.31	$61.30	$61.30
Purchase #7	$46.59	12.245%	$52.2949	$52.29	$52.30	$52.30
7 purchase totals =	$476.78		$514.4781	$514.47	$514.45	$514.50